Cold forging is one of the most reliable metal forming processes on the market. The level of accuracy and precision offered by this method is something few other forming methods can match. Common in mass production, cold forming, also known as cold forging, is an energy- and cost-efficient way to produce huge quantities of product. Yet, with any mass production method, ensuring consistent quality is crucial.
The cold forging process combines compressive forces with shaping dies and other tools, shaping a work piece into its final form. Though the process may seem simple and straightforward, any error can be costly. Variations in the material, die or compressive force can result in a defective part. Such defective parts are unacceptable to us here at STS Intelli, so it's important we ensure the quality of each of our products. We scrutinize our parts and processes through two methods — quality control and quality assurance.
The Basics of Quality
To understand how we guarantee quality in our custom cold forged parts, it’s first important to understand the basic principles of quality. This includes being able to differentiate quality control from quality assurance. We define these terms below:
- Quality Control (QC): Quality control describes a method of inspecting products after they are completed. Usually, internal quality control workers use a series of tests, assessing the final quality of the product. The intention of this process is to confirm that each product meets both industry standards and the standards established between the manufacturer and the client.
- Quality Assurance (QA): Quality assurance involves analyzing the process of production. Instead of looking at the product, quality assurance watches production processes to make sure the right things are done the right way. Usually this involves the analysis the equipment involved in the production process. Formally, quality assurance is tested by a certified professional or firm. It's good practice to also run informal quality assurance checks with internal inspectors on a regular basis.
Most companies use both quality control and quality assurance methods to ensure their methods and products meet industry standards. In this article, we’ll discuss quality assurance and quality control methods as they apply to cold forming.
Quality Control for Cold Forming
Cold forging, in short, is a forming process completed while a material is “cold.” This means the metal is below its recrystallization temperature, around 70 degrees Fahrenheit. Used to produce smaller parts, the cold forming method is more precise and accurate than any other. Cold forging features even more benefits over other forming methods, such as minimized waste, improved strength and good surface finishes. The process of cold forging is also much more energy efficient than the processes involved in hot or warm forging.
Despite these benefits, however, the process of cold metal forming isn't perfect. The method brings with it the potential for several defects and imperfections. Though not as varied or vast as those defects associated with hot forging or machining, these defects are still important to identify and rectify. The four most prominent defects associated with cold forming include:
- Fracture: Fractures, in this case, are cracks or serious structural weaknesses in the interior or at the surface of a product. Fortunately, these defects tend to be the easiest to spot, as it takes a quick visual check to identify breakage at the surface. Internal fractures usually come to light during product stress testing. In any of these cases, the cause is usually more stress or friction than the material can handle. Avoiding these fractures involves adjusting the cold forming process to better suit the work material.
- Surface Imperfections: Roughness, scratching, scoring or other problems at the surface of a product are surface imperfections. Such imperfections are usually the result of improper lubrication or die surface imperfections. Contamination is another potential source. Surface defects can also be the result of, or contribute to, other imperfections, such as fractures and flow imperfections.
- Flow Imperfections: When the shape of the product as a whole is incorrect, this is a flow imperfection. This can include material folding, under filling, flashes and buckling, among other imperfections. Usually, these flow imperfections are the result of an issue in the process or the material. Poorly designed dies, incorrect quantities of material or incorrectly placed materials are a few examples.
- Changes in Properties: Changes in the physical properties of a material do happen in cold forming, though this tends to be rare. Decarburization and martensite formation are a couple of examples.
Usually, quality control staff can identify such imperfections with basic visual and stress tests. However, all they can do after identifying an imperfection is to remove the part from the batch and either scrap or recycle the material.
While checking parts for defects is always a necessary part of a company’s promise for quality, optimizing the process to produce fewer defective parts is as important. Such optimization can make the manufacturing process more efficient, both in energy and in cost. Each defective product created means more material scrapped or recycled. It also means the energy used to create these unusable parts was wasted. Quality assurance helps to avoid this.
Quality Assurance in Cold Forming
By its nature, the cold forming process can produce defective parts. This is especially true when the process contains mistakes. Quality assurance for cold formed components helps avoid such defects by analyzing and optimizing the manufacturing process. This helps to produce consistently successful results.
Assessing and designing processes in such a way involves a great deal of planning and work. However, consistent quality helps reduce the costs associated with defective parts and reduces the stresses put on quality control personnel. Some of the quality assurance practices commonly used include:
- Thorough Equipment Preparation: It seems simple, but too many companies overlook this part of the quality assurance process. Basic issues, such as surface quality defects and damage, can easily be avoided with simple visual checks, cleaning processes and basic machine calibrations. Visual checks simply involve looking over the surfaces of the presses and dies for dust and contaminants. Routine cleaning of these same parts to remove dust, debris and leftovers from any die-machining processes is just as important. Additionally, regular calibration and recalibration of the tooling machines and presses involved in the cold forming process is necessary to ensure proper machine function during manufacturing processes.
- Computer Simulation: Since the 1980s, the metal forming industry has used computer simulation as a reliable way to predict the outcome of their manufacturing processes. These computer programs use a combination of statistical analysis and modeling to predict the success of a project. Typically, such programs will ask for the geometry of the die and the composition of the material in use. Such data can then be used to calculate strain, strain rate, temperature and potential defects in the part. Computer simulation like this has been used in the past to minimize fracture and flow imperfection. STS Intelli uses sophisticated 3D simulation software just for this purpose.
- Prototyping and Testing: Though computer simulations can help identify most potentially problematic manufacturing processes and material limitations, such simulations often fail to take into account the more mundane aspects of manufacturing. Lubricant choice is one such aspect. Proper lubrication between the die and the material reduces friction between their surfaces, which helps minimize surface and flow imperfections and helps to avoid fractures. Different lubricants react in unique ways for different materials and surface types, so choosing an appropriate lubricant is crucial. The only way to do this is by producing prototypes and test models of the finished products using different lubrication methods.
- Regular Training and Assessment: One of the final aspects of quality assurance is ensuring the quality of the staff. As handlers of the equipment, operators are often the determining factor in assuring the quality of a part. That’s why regularly training your staff and ensuring a sufficient level of knowledge in cold forming techniques is so important to quality assurance.
These quality assurance methods are most commonly used in the industry, but new methods are on the horizon. Neural networks and large databases of expert knowledge are currently under development to provide guidance and simulated expertise for industry professionals. Such technology would allow manufacturers to broaden their pool of expertise and feel more comfortable working with unfamiliar materials, provided they are listed in these databases.
The Difference Between Hot Forming and Cold Forming
With both quality assurance and quality control measures in place, cold forming is one of the best ways to ensure consistent quality at a reasonable price. That’s something no other forming method can claim.
Assuring and controlling quality within cold formed parts is much simpler and easier than it is within hot forged or machined parts. This is primarily due to the increased number of defects and process issues that come with these forming methods. While the potential defects of cold forming include fractures, surface imperfections and flow problems, hot forming and machining methods can result in an even wider range of imperfections.
Hot forging is a process that involves applying extreme heat to a metal, causing the metal to soften. The exact heat of the material depends on the type of metal in use, with temperatures ranging from 700 to over 2,000 degrees Fahrenheit. Though a better forming choice for harder metals, hot forming is less precise and accurate than cold forming and can result in the following defects on top of those involved in cold forming:
- Sprue and Overflow: With any hot forging process, there is excess material. This is because the metal is pushed into a form through a sprue tube. When the form is filled, the leftover material remains in the sprue tube. All this excess material must then be removed from the form once the forming process is completed, which involves machining. Though this overflow isn’t a defect in itself, the subsequent machining process can cause defects.
- Seams: If excess material continues to be pushed into a form, overflow material will start to flow into the cracks between the sides of the form, creating seams. Though this can be removed with extra machining and processing, machining leaves room for more defects, and removing these seams adds to the cost of the part.
- Oxidation: When materials are heated to their melting point or just below it, the energy at an atomic level is substantial. These energized atoms at the surface of a material are more likely to react with the surrounding air, changing the chemical composition of the material at the surface. This can result in embrittlement, among other problems.
Machining is another forming method, which uses a lathe or other cutting machine to create a part out of a larger block of material. While this method is effective, it is more wasteful than either the hot or cold forming methods. It also generates a great deal of waste material and takes a significantly longer amount of time to complete. Machining is commonly used as a secondary method to both hot and cold forming, fixing any major imperfections and removing any excess material. However, machining can result in some defects as well, including:
- Burrs and Surface Imperfections: Since machining involves cutting, small variations in the quality of a cut can have tremendous consequences for the surface quality of a part. However, even the sharpest blades can produce overly sharp edges, called burrs. These burrs are usually removed by blasting the edges of the part, which can result in surface imperfections as well.
- Over-machining: Though automatic machining with a computer system is relatively common today, many manufacturers still use humans to control machines, especially when the job involves detailing or custom work. Removing excess material often falls under this category. Over-machining can become a problem in this case. A mistake on the part of the machinist can result in too much material being removed from the part. Since welding will affect the structural integrity and look of the part, the piece is usually scrapped.
Quality assurance in machining also involves more training and skill building for employees and constant machine calibration and maintenance.
Where to Find Quality Cold Formed Parts
At STS Intelli, we know quality is at the forefront of your mind. When you work with us, you can rest easy knowing you’re working with a company with a long history of customer satisfaction and premier quality. Our customized cold forging processes are uniquely optimized, using specialist knowledge and 3D modeling, to provide you with the consistent quality you need at a price you can’t beat.
In today’s market, businesses demand consistent quality at a competitive price, and that’s what we provide. Our experience covers all industries, from aerospace applications to medical technology. Regardless of the application, with our quality cold forging manufacturing processes, we can guarantee you the best in quality control and assurance.
Contact our STS Intelli team today, and let’s get started discussing your metal forming needs.