10 Things to Consider When Buying Steel Products for Mechanical Manufacturing solution

Quality control in steel products is extremely important. The steel fabrication process demands attention to detail and an understanding of the many variables that come into play.

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When sourcing steel products from another country, you often have no control over the production process and must rely solely on your supplier. Steel inspections can help to reduce risks and ensure that the products meet your quality standards.

In light of this issue, we’ve created an insider guide from our clients’ cases packed with steel quality inspection strategies to reduce your risks when you buy steel from China, India – or anywhere else in the world.

Why Is Steel Quality Inspection Important?

Quality inspections of steel products are important to ensure that the products you’re purchasing meet industry standards and customer-specific requirements. Steel inspections can often help you identify faults or irregularities in the material – even before you receive the products from your supplier- saving you both cost and time.

But not only does it ensure the reliability and safety of the steel, but it can also verify that the produced steel products use a particular grade of steel and meets agreed-upon standards set by industry bodies such as ASTM (American Society for Testing and Materials) or AISI (American Iron and Steel Institute).

What to Consider When Buying Steel Abroad?

The first step is to understand the technical requirements of the products that you’d like to purchase, and be aware that each country has its own standards for steel production. Make sure your supplier can meet your technical requirements, despite what steel standard they have.

What Are the Common Steel Standards?

There are numerous steel standards, each with its own unique grading system and levels. Some of the most common include:

• American Society for Testing and Materials – ASTM
• American Iron and Steel Institute – AISI
• Society of Automotive Engineers – SAE
• Deutsches Institut für Normung – DIN (German Institute for Standardization)
• European Committee for Standardization – EN
• Japanese Industrial Standards – JIS
• China National Standards Committee – GB

Steel Vendor Selection: How to Audit Steel Suppliers

One of the most critical moments in the selection of steel suppliers. Most of the steel producers are located in China, India, Japan and Brazil, and their factories are located thousands of miles away from you. It is important to find a supplier who can meet your needs in terms of quality, specifications, delivery time, and price.

How to Check the Steel Factory?

If the steel vendor you’ve chosen is a manufacturer, then you should consider doing a factory audit. A factory audit often includes: checking the manufacturer’s basic register information and background, bank information, existence and production capability, quality control and management system, human sources and more.

An image of a factory audits summary, click here to see the factory audit sample report.

How to Check a Steel Supplier?

Be aware that many steel traders try to pass themselves off as a manufacturer, especially in China. If you’re questioning whether your vendor is a trader or manufacturer, consider conducting a supplier audit to review the company’s registration information and background.

Steel Supplier Versus Steel Manufacturer, What Is the Best Option?

Both steel manufacturers and trading companies have their advantages and disadvantages.

Advantages and Disadvantages of Buying from Steel Manufacturers

For still mills, they have invested heavily in many fixed assets. Hence, it’s less likely that they would risk cheating. They can also control the production of the order by themselves, making it more likely that they will produce the goods on time and as per the specifications and standards.

On the downside, metal manufacturers often require a higher minimum order quantity and can’t produce multiple goods at the same factory.

Steel Trading Companies Advantages and Disadvantages

The advantages of dealing with steel trading companies are that they are more flexible than manufacturers. For example, they are more likely to collect orders with many specifications and low quantities and can offer alternatives to you.

They are also very familiar with the market, have many sources and can communicate well with steel mills to resolve problems and find the products you require.

Aside from having little to no control over the actual productions, the main disadvantage is that the company may use your down payment to find materials from steel mills and:

• Wait for the market to turn to get lower prices, which can influence their on-time delivery
• Substitute your steel products that are of a foreign standard with ones that have a similar domestic standard.
• Increase the price after your down payment and demand you pay the price difference.

Tips for Selecting the Best Steel Supplier

Below are some tips for choosing the best supplier for your steel products.

• Opt for steel mills – Purchase directly from the manufacturer if your order meets the minimum requirement of order from the steel mills, as they are less likely to cheat on you.
• Beauty can be a red flag – If a supplier has an amazing website, but it’s only in English, and the contact information is just a personal cell number, that should be a concern to consider.
• Deposit payment – Before giving a company any money, we strongly suggest you double-check them through an audit, especially if something doesn’t feel right.
• Be cautious of low prices – Don’t be fooled by cheaper steel options; the lower price is usually indicative of a lower quality product.

Steel Inspection: What Quality Inspection Is Best for Steel Products?

There are four primary types of quality inspections used in quality control; however, when it comes to steel products, the most required inspections are often pre shipment and loading supervision for steel quality control.

The Steel Inspection Checklist: Pre Shipment Inspections

The pre shipment inspection (PSI) of steel products is conducted on a random sample of finished goods and packed on-site to ensure that the products comply with your specifications, or a full inspection (checking all products). The inspector will look at different parameters, including:

1. Style and Quantity Check:  

Check the actual weight of the steel by calibrating the weighting apparatus and quantity check the pieces by counting (especially useful for plates, sheets, tubes and bars).

2. Steel Dimension Check: 

Verify that the dimensions align with the agreed specifications by assessing the following:

• Plates and Sheets Coils: thickness, width
• Bar: diameter
• Pipes: Outside diameter, wall thickness, straightness, ovality and more.

3. Visual Inspection of Steel

Check the workmanship of the produced goods to identify using a visual inspection. This will tell you whether there are any defects such as dents, scratches, uneven weld beads, underfill of weld materials etc. The acceptance of these imperfections is per the applicable standard.

Other Important Pre Shipment Inspections

• Check the manufacturers Mill Test Certificate (MTC).
• Check the chemical composition using a PMI Spectrometer.
• Check the shipping mark and packing check.

Steel Lab Testing Inspections

1. Chemical Composition Test – Used to determine the chemical composition of the steel and measure its quality.

2. Mechanical Property Test (Yield Strength, Tensile Strength, Elongation) – Evaluate the material’s tensile strength, yield point, and elongation percentage.

3. Hardness Test – Check the material’s resistance to local penetration.

4. Ultrasonic testing (UT) of steel – Detect if there are any flaws or defects in the material.

Risks During and After Steel Pre Shipment Inspection

Here are some of the main risks that are associated with a pre shipment inspection.

1. Don’t forget the check the steel grade, the supplier may substitute your steel products that are of a foreign standard with those of a similar domestic standard.
2. It’s important to test the chemical composition to check the authenticity of the materials and compare the testing result with the MTC. For example, some materials may be of lower grade materials (for example, SS201 instead of the required SS316).
3. Ask the supplier to package all the materials on-site when the inspector is present so that they do not try to lower the quantity, especially the coils, which cannot be counted by pieces, after the inspection. Ask the inspector to stick or sign on the package to prevent someone from opening and repackaging the materials.
4. Be aware that some machines may be tampered by the supplier and may give inaccurate readings, especially for those that are harder to calculate on-site, such as steel coils.

Check here one HQTS Steel Preshipment Inspection Sample Report

What Is a Loading Supervision Steel Procedure?

Steel products are of high value. Unfortunately, some suppliers may cheat to make an extra profit. Once the pre-shipment inspection is complete and the inspector has left, your products may still be at risk for replacement or having the quantity reduced by the supplier.

This is where container loading supervision is useful. A loading supervision is conducted to ensure that the cargo has been properly loaded into the container. This inspection includes:

1. Check the quantity and weight.
2. Check the package and label.
3. Check the internal end external conditions of the container.
4. Supervise the loading process and the placing and fixing the products in the container.
5. Sealing of the container and witnessing the container leave.

Tips: Try to witness the container leave the factory after loading and record the license tag of the truck and the container number. Confirm with the driver whether it’s from the shipping company or the agent.

Conclusion Steel Inspection Checklist and Tips to Reduce Risks Quality Risks (Insiders Guide)

The steel market, especially in China and India, is complex, as there are small traders who pose as fraud suppliers. However, most of these suppliers are reliable businesses. Having said that, it’s important to know the risks associated with buying steel abroad.

To mitigate risks, we recommend conducting a supplier audit or factory audit on the businesses, combined with a pre shipment inspection and loading supervision.

Not all sheet metal parts are created equal, and the most important factor in the success of a sheet metal part is the material it’s made from.

The type of metal a sheet metal part is made from must be chosen carefully to ensure that the part meets fabrication requirements during manufacture and performance requirements in its final application. Picking the wrong material can cause part or whole product failure, low yields, high costs, poor performance or a number of safety issues.

Imagine a safety critical structural part failing due to improper material selection, and you have an idea of one potential concern. If you imagine products having to be recalled, at a high cost, due to in-use failure you have an idea of another potential concern.

The process of selecting the material for a sheet metal part can be complex because of the sheer number of factors involved. The issue is something that requires careful consideration.

The most important questions to answer when selecting a material for sheet metal parts are:

1. What requirements will a sheet metal part need to meet in application?
2. What types of sheet metal are available?
3. What fabrication and manufacturing processes are possible with different sheet metals?

Fig. 1: Sheet Metal Parts at Komacut

In this guide, we'll look at the most common sheet metal materials used and go over the factors that need to be considered when choosing the right material.

There are many types of sheet metal, and each type has its benefits and drawbacks that must be considered when selecting a material for a project. The different properties different materials have make them suitable for different applications.

We will explore the types of sheet metal materials used at Komaspec and give examples of real-life uses for each of them.

Mild or Low Carbon Steel

Mild steel is by far the most commonly used material for sheet metal fabrication. The relative strength it has, combined with the ease of fabrication and relatively low cost compared to stainless steel or aluminum, means that it’s suitable in plenty of applications. These steels can be used to create a wide variety of custom steel parts. Automotive body panels, furniture and structural parts are common examples of mild steel in application.

Mild Steel Pros

• Inexpensive
• Easy to work with
• High weldability
• Versatile
• Strong for its weight
• Can support a variety of surface finishes

Mild Steel Cons

• Not suitable for high-gloss polishing
• Needs protection from rust (additional processing and cost)
• Less strong and durable than other materials
• Less heat resistant than other materials

Stainless Steel

Stainless steel is an alloy containing chromium, which provides good corrosion resistance and improved strength. Stainless steel is great in outdoor applications or other applications in which parts might be exposed to rust or corrosive chemicals. It’s also useful in applications that need more hardness than mild steel. As well as this, it is non-magnetic and non-sparking, making it ideal for medical instruments.

Fig. 2: Mill Finish – Stainless Steel

Stainless Steel Pros

• Easy to work with
• Suitable for high-gloss polishing
• Durable
• Easy to clean and sterilize
• High levels of built-in corrosion resistance

Stainless Steel Cons

• More expensive than mild steel (average of three to five times the cost, depending on the grade of stainless steel)
• Welding can be more cumbersome (requires specialized equipment)
• It cannot be used in applications where magnetism is needed

Galvanized Steel

When steel is galvanized, a layer of zinc is bonded to its surface. This method serves as a cost-effective way to build a high level of corrosion resistance into the material. In turn, this reduces the potential for rusting prior to fabrication and the need for additional surface finishing. Galvanized steel is perfect for things like fencing and other outdoor frameworks that are exposed to the weather.

Fig. 3: Cold Galvanized Steel

Galvanized Steel Pros

• Easy to manufacture and maintain
• Cost-effective corrosion protection
• Durable

Galvanized Steel Cons

• Joints or cuts can corrode over time where the processing (laser cuts or bending in the case of sheet metal fabrication) has compromised the galvanized protective layer.
• Galvanized steel can be expensive. It is significantly more expensive than mild steel, for example.

Aluminum

Aluminum has many wonderful qualities. Its primary qualities are its high level of resistance to rust and its reduced weight, being one-third of the weight of steel. It is less strong than other materials, but this can sometimes be overcome through design. In some applications, aluminum can also be designed to be equally as strong as steel.

Because of its lack of strength, aluminum may often not be able to handle the same stresses as steel. As such, you might want to contact our representatives at Komaspec to help you decide if aluminum is suitable for your intended use or not.

Fig. 4: Aluminum RAL

Aluminum Pros

• High strength to weight ratio (ideal for applications requiring weight reduction)
• Truly corrosion resistant
• Durable
• Aesthetically attractive with only minor polishing

Aluminum Cons

• More expensive than carbon steels
• Significantly lower tensile and yield strength than steel
• Can require additional hardening processes after initial manufacturing stage

Spring Steel

Spring steel is a very resilient material containing manganese and high concentrations of carbon. It is designed to bend or flex under load and to return to its original shape when the load is removed. This makes it an excellent choice for making latching mechanisms, drive belts and, of course, springs.

Spring Steel Pros

• High yield strength
• High tensile and fatigue strength
• Easily formed and shaped

Spring Steel Cons

• Potential to lose shape over time
• Prone to rust and corrosion
• Limited heat resistance

For more info about each of the sheet metal materials Komaspec offers, including specific physical properties and surface finishing options, you can refer to the sheet metal material selection on our website.

Order and track sheet metal components online through Komaspec's on-demand sheet metal fabrication platform.

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The costs that come with sheet metal parts fabrication begin with the cost of the raw material. Costlier materials, such as aluminum, stainless steel, and copper, can provide superior performance compared to cheaper materials, such as mild steel and galvanized steel. Still, they obviously come with a higher price tag.

In some cases, a cheaper metal will be suitable for a job and will provide adequate performance at a lower cost. For example, if aluminum is too expensive for a part that requires light weight and corrosion resistance, galvanized steel might be a better choice.

Link to Muchang

Additional reading:
5 Things to Know Before Buying Welded Steel Pipes

Ultimately, choosing the right material will mean weighing up performance requirements and the cost constraints of a project.

The table below shows a rough outline of how much each material costs. We can see that, while aluminum is twice as expensive as steel per kg, stainless steel is nearly five times more costly. Titanium is much more expensive again and is used sparingly in products such as jet engines, where the extra strength it provides is crucial.

Fig. 5: Material Cost Per Kg (USD)

The Difficulty in Comparing Material Costs

When considering which sheet metal material to buy for a project based on cost, there’s more to consider than just the price of a material per kg. You have to weigh material cost per kg against the design and performance goals of the project. Not all sheet metal is created equal in strength, weight, and appearance.

Stainless steel is stronger by weight than aluminum, for example, meaning that designs can be adapted. Thinner stainless steel can be used for a tank or vessel than it can for an aluminum one, for example.

Cost Increase of Custom Steel Parts

Custom design requirements often impact the price of steel sheet metal parts. This is because custom designs often require more intricate processes and skills to manufacture, increasing the cost of labor and materials.

Custom metal parts fabrication often also requires additional processes, such as welding, cutting, and bending, which can also increase the cost of the parts. They may require the use of specialized tools and equipment to construct correctly as well.

Understanding the mechanical properties different sheet metals have and the effect these properties have in application is critical to selecting the right material. There are many physical qualities inherent in different metals, and each one can be used to serve a different purpose.

Some of the most essential mechanical factors to consider in the material selection process include:

• Strength
• Ductility
• Corrosion resistance
• Ease of manufacture

Strength of Sheet Metal Parts

Material strength is often the most widely used metric in determining material suitability. It is measured according to how much load a material can withstand before it bends out of its original shape. This bending is also known as plastic deformation.

There are two ways of looking at the strength of a material when it comes to choosing one for manufacture. Considering each separately may give a different outcome in decision making.

Strength By Cost

This simply considers how strong a material is in respect to how much it costs. Titanium is an example of a material with a high cost to strength ratio, and mild steel is an example of the opposite.

For metal enclosures or tanks that require large amounts of high strength material at low cost, for example, low-carbon (mild) steel would generally be considered the ideal material.

Strength By Weight

This considers how strong a material is in relation to its mass (or weight). Gaining high strength with lightweight materials is important in certain applications. In airplanes, for example, reducing weight is essential, and aluminum is often a good choice.

Strength to weight properties are also assessed by looking at specific strength.

Interestingly, in a comparison of aluminum, carbon steel, and stainless steel, the aluminum alloy has the highest specific strength (ASM Material Data Sheet), despite having the lowest tensile strength.

Fig. 6: Tensile Strength vs. Specific Strength

Ductility

Also referred to as formability, this is the ability of a material to be stretched without cracking or breaking. If a material is highly ductile, it will withstand a large amount of stretching. Stretching commonly occurs in manufacture when a tight radius is formed during a metal stamping or folding process.

Fig. 7: Sheet Metal Materials at Komaspec

A simple way to visualize ductility is to imagine a material acting as a spring - the greater the elasticity of a material, the better its ductility. One thing to note is that this flexibility can be increased using a metal-forming process called annealing.

Corrosion Resistance

Corrosion occurs when a metal deteriorates as a result of the action of air, moisture or a chemical. The most common form is rust, which happens when iron in a material reacts with the oxygen and moisture in its surroundings. Good corrosion resistance (Metals - Corrosion Resistance to Aggressive Fluids) is a crucial factor in sheet metal selection because corrosion can weaken steel in a surprisingly short period of time if the conditions are right.

Fig. 8: Corrosion From Aggressive Fluids

The two main factors that help reduce corrosion are:

1. Choosing a material that will not be prone to corrosion in the application the part will have
2. Employing a secondary finishing process such as painting or galvanizing

What is the Best Material for Corrosion Resistance?

Stainless Steel

Stainless steel contains chromium, which forms a thin film of chromium oxide on its surface, protecting it from corrosion. Stainless steel can become discolored, or it can rust if there is long term exposure to the elements. It is particularly vulnerable to corrosion where there are high salt concentrations. However, the resistance is greatly superior to mild steels.

Bimetal corrosion is a risk with stainless steel and must be considered when mating with other parts or fasteners.

Aluminum

A lightweight alternative to steel, aluminum is a naturally non-reactive metal that will not corrode in the presence of air or water.

Aluminum can be somewhat vulnerable to corrosion when in contact with concrete, however, and there’s also a risk of bimetal corrosion. Both of these problems can be overcome through anodizing or painting.

Modified Mild Steel

Using galvanized mild steel could be a great alternative if cost is a factor. The Zinc coating gives a layer of protection at lower cost. Be aware, however, that when galvanized mild steel sheets are cut, the edges are exposed and will be vulnerable to rust.

Mild Steels

Mild carbon steels without secondary finishing will rust rapidly in the presence of moisture or salt. In fact, unprotected steel sheets can begin to rust even before fabrication, which often leads to the need for deburring or chemical treatment to remove rust before surface finishing.

Rust can be so severe, in some cases, that it impacts the final part appearance even after painting. Parts can appear “mottled” or like they have a blotched surface when this happens.

Sheet metal part fabrication processes involve procedures such as cutting, bending, and joining sheets of metal. These procedures create different configurations of sheet metal to create custom steel parts. Each material has its own specific advantages and disadvantages in the fabrication process that need to be considered.

Laser Cutting

Laser cutting is a precise and reliable method for cutting all different types of metal. This method is a great option in many different situations. However, it’s particularly useful where speed and precision are important, such as in the automotive industry. Lasers are also useful for cutting thicker materials, for making complex cut-outs and for making very clean cuts.

Shiny metals, such as aluminum and copper, are more difficult to cut, although it is still possible to cut these materials with a laser. The minimum / maximum thickness which can be cut, however, varies depending on the material type, which in the case of very thick or very thin material, may limit potential choices.

Bending

There are two factors that have an impact on bendability:

1. Material Choice

Some materials can be bended more easily than others and with more success in application. It’s worth noting, however, that even within the same material, there can be differences in bendability between different grades. If ductility is important, for example, the series aluminum is best avoided as the hardness of the material can result in micro-cracks and part failure duing bending.

Generally speaking, aluminum is commonly considered a good choice where sheet metal bending is required.

1. Product Design

Designs with tight bend radii and low tolerances will mean that a more bendable material is required. For more about bend design, read our article on sheet metal design guidelines. Very stiff materials (i.e. medium carbon or stainless steels) may require larger reliefs are larger bend radii vs mild steels and aluminum parts.

Fig. 9: Metal Bending at Komacut

Weldability

Welding is one of the most common methods for joining and manufacturing metal components. This process uses a high-powered and highly controlled electric arc to heat base metals to the point where they melt. They are then joined and solidify as almost one piece.

The weldability of sheet metal will depend on the type of filler metal used, the process used and the material makeup of the sheet.

Mild carbon steels are highly weldable with a variety of processes, are generally finished with secondary processes which help to resolve discoloration of the base material.  Aluminum requires TIG welding, which can be more time and cost intensive than MIG, and the material is more vulnerable to deformation and discoloration due to heating during the welding process. Stainless is also weldable, but requires TIG or special robotic welding equipment and may need passivation or secondary processes to hide discoloration from the welding process.

Fig. 10: Robotic Welding at Komacut

Different materials have different properties when it comes to surface finishing. Not all materials are compatible with all surface finishing options, such as anodization being largely specific to aluminum, or the difficulty of electropolishing mild steel parts.

For which options are available for various sheet metal materials, please see the table below or explore in greater detail in our surface finishing article.

Finish Corrosion Resistance Coating Thickness Abrasion Resistance

Table 1: Surface Finishing: Corrosion, Thickness, Abrasion

Finish Carbon Steel Stainless steel Aluminium Application Visual Requirements Thickness Corrosion resistance Mill Finish Internal Parts or Parts with Subsequent Processing Low-Visual - - Antirust Oiling Parts with Subsequent Processing Low-Visual - 24 Hours NSS Brushed Indoor Med-Visual - - Anodized Indoor / Outdoor High-Visual - - Mircro-Polishing Indoor / Outdoor High-Visual - - Passivation Indoor / Outdoor Med-Visual 0.5 to 15μm - Zinc Plating Indoor / Outdoor Low-Visual 5 to 25μm 48 to 94 Hours NSS E-Coating Indoor / Outdoor Low-Visual 5 to 25μm 96 Hours NSS Powder Coating Indoor / Outdoor High-Visual 70 to 150μm 480- Hours

Table 2: Metal Finishing Guide

The application of the part often determines the finishing requirements. Some reasons for wanting an enhanced surface finish include:

• Aesthetics
• Hygiene
• Durability

Because these aspects are critical to quality for many applications, it’s important to think about these requirements when selecting a material.

Aesthetics

Polishing is a common technique used to create a high-quality look that’s pleasing to the eye. The process involves progressively removing all surface imperfections to give a metal part a shiny finish.

Fig. 11: Surface Finishing

Polishing for Sheet Metal Parts

• Copper
• Stainless steel
• Aluminum

Stainless steel can be brought to a mirror finish and is very durable; aluminum is less durable and can take longer to reach the same finish. It is not possible to create a durable polished surface on mild steel.

Hygienic Sheet Metal Parts

Sheet metal parts are often used in both the food industry and medical settings. The material chosen must be resistant to the build-up of bacteria and other contaminants.

Stainless steel, for example, is a popular choice for sheet metal products because it is non-porous and resistant to corrosion. This eliminates the need for potentially toxic paints and other coatings.

Additionally, stainless steel can be easily cleaned and sterilized using various chemical and thermal methods. This makes it an ideal choice for food-grade products and medical instrumentation.

Stainless steel 316, for example, is widely used for food service or medical equipment due to its excellent resistance to chemical cleaning agents, acids and other corrosion.

Durability for Sheet Metal Parts

Durability is the main factor that affects a material’s resilience to dents, scratches and bending. Also important in hygienic environments, the durability of a material affects how well it can withstand harsh environments without needing to be repaired or replaced.

Stainless steel is a great option if a part needs to resist scratching and be easy to repair. When scratched, it does not cause possible contamination with aluminum oxide. Aluminum, along with copper, will resist scratches and deformation very poorly.

Mild steel is another durable material, but the paints and coating needed should be considered as they can often lead to the same problems with contamination.

Material finishing requirements will help determine the best material choice for any particular part. For more about different types of finishing, read this guide.

For more information, please visit Steel Products for Mechanical Manufacturing solution.