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How to choose the right material for CNC machining

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There are hundreds of metal alloys available for CNC machining. Which one is best for your next project depends on a number of factors, including price, workability, corrosion resistance, strength, weight and aesthetic appearance. To help you choose, here’s a closer look at the ones we use every day and what benefits they may have for your next project.

 

Aluminum 7075
7075 is a superior grade of aluminum, alloyed primarily with zinc. It is one of the strongest aluminum alloys, with excellent strength that allows it to regain its original shape when cold formed. 7075 is machinable and can be anodized.
7075 often hardens to T6. However, it is a poor choice for welding and should be avoided in most cases. We typically use 7075 T6 to make plastic injection molds. It is also used for high-strength equipment, such as automotive and aircraft frames and other stressed parts.
Brass
Brass is an alloy of copper and zinc. It is a very soft metal and can often be machined without lubrication. It is also highly functional at room temperature, so it is often used in applications that do not require high strength. There are many types of brass, depending largely on the percentage of zinc. As this percentage increases, corrosion resistance decreases.
Brass has a high luster and closely resembles gold, which is why it is often found in cosmetic applications. Brass is electrically conductive but not magnetic, can be soldered and can be easily recycled. Another characteristic of brass is that it does not spark when struck with another metal, which is why it is used in tools in potentially explosive environments. Interestingly, brass has natural antibacterial and antimicrobial properties, and its use in this regard is still under study.
Brass is common in plumbing fixtures, decorative home hardware, zippers, marine hardware and musical instruments.
Magnesium AZ31
AZ31 magnesium is an alloy with aluminum and zinc. It is up to 35% lighter than aluminum, with equivalent strength, but it is also slightly more expensive.
Magnesium is easy to machine, but it is very flammable, especially in powder form, so a liquid lubricant must be used for CNC machining. Magnesium can be anodized to improve its corrosion resistance. It is also highly stable as a structural material and is an excellent choice for die casting.
AZ31 magnesium is often used for aircraft components where light weight and high strength are most desirable, and can also be found in power tool housings, laptop cases and camera bodies.
303 Stainless Steel
There are many varieties of stainless steel, named for the addition of chromium that helps deter oxidation (rust). Because all stainless steels look alike, great care should be taken to test incoming raw material with metrology equipment such as OES detectors to confirm the characteristics of the steel you are using.
To improve its CNC machining, sulfur is added, but it also reduces its corrosion protection.
303 is not a good choice for cold forming (bending), nor can it be heat treated. The presence of sulfur also means it is not a good choice for welding. It has excellent machining properties, but care must be taken with speeds/feeds and sharpness of cutting tools.
303 is often used for stainless steel nuts and bolts, fittings, shafts and gears. However, it should not be used for marine grade fittings.
304 Stainless Steel
This is the most common form of stainless steel, found in a wide variety of consumer and industrial products. Often called 18/8, this refers to the addition of 18% chromium and 8% nickel to the alloy. These two elements also make the material especially tough and non-magnetic.
304 is easy to machine, but unlike 303 it can be welded. It is also more resistant to corrosion in most normal (non-chemical) environments. In machining it must be processed with very sharp cutting tools and not contaminated with other metals.
Stainless steel 304 is an excellent choice for kitchen accessories and cutlery, tanks and pipes used in industry, formula architecture and automotive moldings.
316 Stainless Steel
The addition of molybdenum makes 316 even more resistant to corrosion, so it is often considered a marine-grade stainless steel. It is also tough and easy to weld.
316 is used in architectural and marine fittings, for industrial pipes and tanks, automotive moldings and kitchen cutlery.

 

1045 carbon steel
This is a common grade of mild steel, i.e. non-stainless. It is usually less expensive than stainless steels, but is considerably stronger and tougher. It is easy to machine and weld, and can be hardened and tempered to obtain different hardnesses.
Steel 1045 (in the European standard, C45) is used in many industrial applications, for nuts and bolts, gears, shafts, connecting rods and other mechanical parts that require a higher degree of toughness and strength than stainless steel. It is also used in architecture, but if exposed to the environment, it is necessary to treat its surface to prevent oxidation.

 

Titanium
Titanium is known for its high strength, light weight, toughness and corrosion resistance. It can be welded, passivated and anodized to increase protection and improve its appearance. Titanium does not polish particularly well, is a poor conductor of electricity but a good conductor of heat. It is a hard material to machine and special tools must be used.
Titanium is generally biocompatible and has a very high melting point. Although it is more expensive than other metals in commercial form, it is actually very abundant in the earth’s crust but difficult to refine.
Titanium works well for metal 3D printing(sintered). It has applications in aerospace, military, biomedical and industrial fields, where it resists heat and corrosive acids well.

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Vacuum Casting in Silicone Molds for Prototyping in the Automotive Industry

Vacuum casting in silicone molds is an essential process in the automotive prototyping industry. It enables the fast and accurate production of plastic and elastomer parts that are essential for the development of vehicle prototypes. In this article, this process, its advantages and its importance in the automotive sector will be described in detail.

Vacuum Casting Process in Silicone Molds:

Vacuum casting in silicone molds is a manufacturing process used to reproduce plastic or rubber parts from a master prototype. The process involves the following steps:

  1. Creation of the master prototype*: Initially, a master prototype of the desired part is created using techniques such as 3D printing or CNC machining. This master prototype will serve as a model for series production.
  2. Silicone mold making*: The master prototype is used to create a high quality silicone mold. This mold will be the negative of the final piece.
  3. Preparation of casting material*: The appropriate material, such as polyurethane resins, is selected for casting. These resins are chosen according to the properties required for the final part.
  4. Vacuum casting*: The casting material is poured into the silicone mold, which is placed in a vacuum chamber. The chamber is evacuated to eliminate any air bubbles and ensure uniform distribution of the material in the mold.
  5. Curing and cooling*: The mold undergoes a controlled curing and cooling process to allow the material to take its final shape and reach its desired mechanical properties.
  6. Part removal*: Once the material has solidified, the final part is removed from the silicone mold. This process is repeated as necessary to produce multiple copies of the part.

Advantages of Vacuum Casting in Silicone Molds:

This process has several advantages in the automotive prototyping sector:

  1. – Speed: Vacuum casting enables the rapid production of prototypes, accelerating vehicle development.
  2. – Accuracy: The manufactured parts are highly accurate and reproducible, which is essential in the design phase.
  3. – Wide range of materials: Different materials can be used to simulate the properties of the final parts, which facilitates the evaluation of prototypes.
  4. – Cost-effectiveness: Compared to other manufacturing techniques, vacuum casting is a relatively inexpensive process.

Applications in the Automotive Sector:

In the automotive industry, vacuum casting in silicone molds is used for the prototyping of interior and exterior parts, such as control panels, headlights, bumpers, and other components. It allows design engineers to evaluate and refine their designs before investing in expensive tools for mass production.

Conclusion:

Vacuum casting in silicone molds is an essential technique in the development of prototypes in the automotive industry. It provides an efficient and accurate way to produce plastic and elastomer parts, speeding up the design process and reducing costs. Purchasing engineers play a key role in selecting the right suppliers and materials to ensure the success of this process in the automotive industry.

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TIPS FOR MOVING FROM PROTOTYPING TO MASS PRODUCTION

Rapid prototypes help you test your design appearance and performance. You can test multiple material options and evaluate your potential market without a large investment in time and money.

Once you are satisfied with your product and are ready to move from prototypes to production, there are several things to make sure of to ensure that the transition to larger volumes is smooth. From PROTOSPAIN we give you five tips to help you optimize the process of bringing your product to market.

1. Choose the right manufacturing process

Metal products

Metal prototypes are generally made by CNC machining or metal 3D printing. Although excellent for some types of prototypes, metal 3D printing is not suitable for production in many cases. Although the technology is advancing, it is still too slow and expensive for larger volumes unless you require complex geometries and lightweight parts.

Most metal prototypes are made by CNC machining and this is a good way to scale volumes over time as demand increases.

For high volume manufacturing, consider die casting. This is the fastest and most economical way to make large batches of identical metal parts. Note that there are design rules for fabrication that must be followed for casting, and you will need to invest in a production tool. But this cost can be recovered in a large production order.

For flat parts, they can opt for laser cutting, which in turn can be bent into three-dimensional shapes. Another technology is stamping and embossing.

Plastic products

If the prototype was made in plastic, it was probably made by 3D printing, CNC machining, polyurethane vacuum casting(Injection molding in silicone molds) or Reaction Injection Molding (RIM) if they are large parts. For larger volumes in plastic, the ideal solution is plastic injection molding.

If the prototype was made in plastic, it was probably made by 3D printing, CNC machining or polyurethane vacuum casting(Injection molding in silicone molds). For larger volumes in plastic, the ideal solution is plastic injection molding.

Injection molding, like die casting, requires strict adherence to design rules that do not come into play when using rapid prototyping techniques. These include the use of ribs and protrusions, minimum wall thickness dimensions, demolding angles, injection point positions, slides, ejector pins and many other considerations.

Therefore, product developers must ensure that their plans take into account the additional cost and time-to-market involved in a transition from one process to another.

2. Prepare a bill of materials (BOM)

Prototypes generally involve only a few finished parts and these have a high unit price.

When it is time to go to production, every element of the assembly must be considered. Every nut, bolt and screw, rubber button or metal clip, even the amount of paint or glue, should be accounted for as a separate cost. More components mean a more complex supply chain, so it pays to keep the design as simple as possible.

Finally, a detailed bill of materials can help you evaluate the amount of labor involved in the assembly process, which can be a significant cost factor.

3. Choose the right material

Sometimes, a prototype is made of an expensive or “exotic” material. This is done to make it a showpiece or to help with a marketing or funding campaign. But exotic materials are not a good choice for high-volume manufacturing.

You should consider using the most common raw materials. They will be less expensive and easier and faster to acquire. More importantly, manufacturers have more experience working with stock materials, so it will be easier to control the process parameters for more reliable results.

4. Choose the right surface finish

A carefully sanded, polished and hand-painted prototype with a custom color certainly looks great. But is that practical on a large scale? Elaborate surface finishes tend to require a lot of attention to detail and careful handwork, something that is not always possible for mass production.

If you need specialized finishing processes, we recommend that you find ways to automate or adhere to one or two finishes rather than multiple finishes. For aluminum parts, anodizing is an attractive and very durable surface treatment and parts can be processed in batches as required without compromising any minimum volume.

5. Certification and testing plan

Unlike prototypes, production parts for commercial sale must be certified under a variety of safety and regulatory schemes. This will depend on many factors, including the environment in which the product is used, whether it runs on electricity and the country where it is sold.

You should be prepared to send finished products to different organizations to obtain certifications and estimate the time and expense of this necessary step.

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How to choose the right plastic depending on its use?

When developing a new product, there are many different types of plastic available for use. The choice of the correct one depends on the specific criteria of each application.

In our experience, developers should consider whether the plastic material is food grade, impact resistant, flexible, engineering grade, fire retardant or biocompatible. The following are our recommendations on the most common plastics used for each product requirement.

Food plastics

Plastics used for food production, cooking and storage must meet certain criteria. They must be sterile and not transfer any flavor to the food. They should be non-biodegradable in most cases, non-absorbent and impervious to edible oils and acids.

PET (polyethylene terephthalate) is almost ideal in all these categories, which is why it is the most common plastic for food packaging. It is found everywhere for use in water and soft drink bottles and other food containers. It is strong and unbreakable, but also lightweight and easily recycled. PET, in fiber form, is called polyester and is the most common type of man-made fabric for clothing and insulation.

LDPE (low density polyethylene) is used to make food bags and cling film, while HDPE (high density polyethylene) is ideal for plastic cutting boards. PP (polypropylene) is also found in food packaging, such as yogurt cups.

It should also be noted that many engineering grade plastics are also considered food safe, but are only used in food processing equipment or other durable products due to their higher cost.

Impact resistant

Plastic in this category must withstand repeated shocks and return to its original shape without denting or cracking.

ABS (acrylonitrile butadiene styrene) and HIPS (high impact polystyrene) are used to manufacture power tool housings, tool boxes, luggage, sporting goods and other products that take a lot of abuse but remain rigid. These resin composites can be made even stronger with the addition of fiberglass or carbon fiber.

There is also a large market for transparent plastic as a replacement for glass. PC (polycarbonate) is ideal for motorcycle windshields, plastic eyeglass lenses and lightweight protective shields.

Flexible

All plastics have some degree of flexibility. Many products do not require high strength, but must be flexible without losing their shape completely.

PP (polypropylene) is the king of plastics for making living hinges such as those found in shampoo bottle caps or pill dispensers. This type of plastic can be bent thousands of times before it breaks within the life of the product.

HDPE is more durable for heavy use, so it is found in heavy-duty trash cans that are thrown away a lot. TPU (thermoplastic polyurethane) is a type of elastomer. It is elastic and rubbery, so it is used for wheels, sealing rings and gaskets, cable housings and sporting goods. The degree of softness and elasticity is controlled by varying the chemical composition.

Engineering degree

Engineering plastics are crystalline polymers with mechanical properties similar to metal. They are strong and durable like their metal counterparts, while being lightweight and less expensive to produce in large production volumes as we do at Protospain.

This category includes plastic materials such as ABS, Nylon (polyamide), PEEK (polyetheretheretherketone) and POM (polyoxymethylene). All are rigid, temperature resistant and low friction. In addition, PEEK, ABS and Nylon can be 3D printed for even more design options.

Some products made from engineering plastics include ball bearings, gears and shafts, knife handles, plastic gun bodies, switches and other weight-saving parts for automotive and aerospace applications.

Fire retardant

In the presence of a flame or other high heat source, any plastic will melt and some will catch fire. Concern for fire resistance is especially important when plastic is used in a confined space such as the interior of an automobile or the cabin of an airplane.

However, plastics vary in their response to fire. Some are self-extinguishing when the heat source is removed. Others may spread flames vertically or produce hazardous fumes.

The most naturally fire resistant plastic is PVC (polyvinyl chloride). The presence of chlorine helps to strip the fire of oxygen needed for combustion, but, of course, chlorine gas is another serious problem.
The secret to fire resistance is to coat the plastic material with a flame retardant chemical or add impurities to the compound that will help interrupt the combustion cycle. Some of these additives include boron, antimony, chlorine, bromine, aluminum and phosphorus. Because there are so many variables and formulations, it is best to check with the manufacturer to confirm what UL fire safety rating the material has. The highest rating is UL94-VO, which means that the material will not burn, is self-extinguishing and will not drip when melted on the ground.

Biocompatible

The use of plastic components for medical devices and equipment has increased considerably in recent years. To protect patients and regulate the industry, ISO-10993 helps to codify the various medical uses of plastic material.

Resins can be used to manufacture blood stents, artificial joints and bone replacements, catheters, prostheses, infusers, cardiac monitors, valves, tubing, pill dispensers and many more.

It is essential to use the right resin for each application. The ISO guidelines determine the assessment of “biohazard” based on the interaction with the body: permanently implanted, in temporary contact with the skin or for use in medical devices.

Based on these categories, we can suggest the following:

– Short-term contact and skin contact: PE, PS, nylon, PVC, Teflon, PEEK, PP, PPSU
– Long-term contact or internal medicine: PPSU, HDPE, PMMA, epoxy (for dental implants)
– Medical equipment and tools: PEEK, POM, PMMA, PC, PVC, HDPE

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What finishes can be done on rapid prototype parts?

Rapid prototyping technologies such as 3D printing, CNC machining, laser cutting and injection molding can produce parts with different surface finishes depending on the manufacturing method and materials used. Some of the most common surface finishes that can be made on parts manufactured using rapid prototyping technologies are described below:

  • Natural finish: This is the most basic finish and refers to the surface of the part as it is produced after the manufacturing process. This finish is typically rough and may have coatings marks, support lines and other fabrication details that are removed in more advanced finishes.
  • Sanding: Sanding is a process that involves the manual removal of surface marks and roughness from the part by the use of sandpaper or sanding tools. The end result is a smoother, more uniform surface.
  • Polishing: Polishing is similar to sanding, but involves a more advanced process that uses polishing tools and abrasive compounds to produce an extremely smooth and shiny surface. This finish is common on parts that require an attractive aesthetic appearance, ranging from a very fine matte finish to a mirror polish. This technique is used for the manufacture of transparent parts.
  • Blasting: This is a finishing process that uses compressed air and abrasive material to remove marks and roughness from the surface of the part. This process can produce a uniform, matte surface, similar to the finish of die casting.
  • Painting: Paint finishing involves the application of a coat of paint on the surface of the part to improve the aesthetic appearance and durability. This finish is common on parts used in consumer and design applications.
  • Anodizing: Anodizing is an electrochemical coating process commonly used on aluminum parts to improve corrosion resistance and aesthetic appearance. This process produces a layer of aluminum oxide on the surface of the part.

In short, there are many different surface finishes that can be made on parts manufactured using rapid prototyping technologies. Each finish has its own advantages and disadvantages, and the choice will depend on the type of part being manufactured and its intended function. It is important to choose the right finish to ensure that the part has the desired appearance and durability.

From Protospain we can give you the necessary advice to choose the most suitable surface finish for the use you are going to give to the prototype. Do not hesitate to contact us for further information.

 

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