January 5, 2022

CNC Machining Vs Injection Molding

What is CNC Machining

CNC machining is computer software controlled the movement of factory machinery and tools. The manufacturers can produce parts in less time, reduce waste, and reduce the risk of human error.

This manufacturing process controls a wide variety of complex machinery in this article. CNC machining makes it possible for three-dimensional cutting. It follows a programmed guide.

CNC machining pays well and has excellent long-term employment prospects. The work is interesting, and you do not need a college degree to get started. CNC machining is easy to learn and takes passion and willingness.

The career combines manufacturing and technology. The idea of doing highly skilled work on complex machines makes it interesting. Work with your hands and different materials and the satisfaction of creating something tangible.

The process is run by the CNC machine computerized controls and machine tools used for removing layers of material from a stock piece. The stock pieces come either in wood, plastic, glass, or metal. A CNC machine allows precision and accuracy in the production runs.

Learning CNC machining depends on your attitude. Dealing with machines is not a walk in the park, but if you pay attention to the instructions, you will find your way. It becomes less straining.

Put on hard work and determination, you will pull through. The CNC machining training program ensures that you are prepared to tackle the job.

Positive results will yield the above qualifications and expectations. The CNC program works in stages, and there is a standard program that teaches you the basics of CNC machine operation. It is easy for you to quickly grasp the concepts and helps you understand basic math. The intermediate programming skills take a year, and the advanced one takes years.

Using the CNC machine does not mean you have to go way out of your budget as you make products. It accommodates many accessories for any use. They range from small to big items. Even if the professional CNC machines are not affordable, if it brings money, it is worth it. You still get low-budget CNC machines that you can afford as a beginner, amateur, hobbyist, and DIYer.

Pros

  • Consistency
  • Easy to learn
  • Advanced
  • Continuous use
  • Flexibility

Cons

  • Not affordable
  • Minimal employment rate

What is Injection molding?

Plastic injection molding is whereby molten materials are injected into molds to make parts. Most of the materials are thermoplastics. Before the injection, the plastic is heated in the barrel. What follows is the injection into the mold, moving along with runners, and then into the part itself.

Once completed, the mold opens, and the part is injected. Repeat the process as you load into hydraulic or electric machines. Proper plastic resin produces precision parts at a fast rate.

It is for intricate parts compared to other techniques. You are allowed to incorporate more features at small tolerances. Hold this molding in the palm of your hand, and it has ribs, metal inserts, side cores, and holes made with a sliding shut-off feature in the tool. These are a lot of features in a small part. It would be impractical to make using plastic fabrication and impossible to make using the vacuum forming process.

The saw comes with high repeatability. When your mold tool is done, identical products can be made again. Mold tools have a very long mold tool life. Treat the molding tool by the molding machine setters.

The molding tool comes at a low cost per part and there is an initial high investment for the plastic injection molding tool. After that, the cost per part is low. Unlike other plastic processing techniques that need many operations, like polishing, injection molding does it all at once. Choosing the CNC machine part above costs hundreds of pounds per part. If you want a full production, injection molding is the way to go.

Cycle times are as low as 10 seconds. It combines that with a multi-impression injection molding tool and gets many products quickly. A lot of features are to be molded correctly. At about 50 seconds, you still get 70 parts per cavity per hour. CNC machining takes longer.

There are a lot of materials available for plastic injection molding. These are standard materials, such as antistatic plastic, thermoplastic rubber, chemical resistant plastics, infrared, bio-compostable with color compounding, or masterbatch coloring. You have an endless choice of colors. The black color is made out of PPO – poly(phenylene oxide), a rigid and flame-retardant material.
As if the colors are not enough, the injection molding tool comes with a finish that shows on the molding. Use any finish you like, for example, leather-look, soft-touch, sparked, or high shine.

You have logos or other text engraved in the tool and your moldings printed. A wide range of inks is available that will print well on plastic. There is high part repeatability for injection molding. The sprues and runners can be reground, and the material reused.

Pros

  • Great precision
  • High repeatability
  • High speed
  • Low cost per part
  • Many choices of available plastics

Cons

  • Not affordable
  • Higher lead time

Equipment Cost Comparison

CNC machining requires the creation of a CAD file and its conversion to being usable for the mill. Injection molding creates a mold, which takes lead time and more money.

Speed

CNC machines go quickly from CAD to creating products. In one place, injection molding can produce parts quicker. For the low volume of parts, CNC machining is the fastest. Making 10 parts in 2 weeks requires CNC machining as your solution.

If you need 50,000 parts in 4 months, injection molding is the way to go. Injection molding requires time to make the mold and ensure the parts are intolerant. Creating parts using the mold is a fast process, and the upfront time investment of injection molding pays off at high volumes.

Volume

When it comes to the price per part, injection molding takes the trophy. Factoring in start-up, CNC milling is affordable for a few CNC parts up to a hundred, hundreds to thousands of parts, plastic injection molding emerges as the choice.

Material

Injection molding covers plastics, including two camps of thermoplastic and thermoset resins, covering everything from everyday plastics like ABS to nylon.

CNC machining offers a range of selection of materials to create the parts. For injected molded components, the material selection is more limited.

Tolerance

CNC machining features more materials. A tighter tolerance can be held, and a better surface finish. The advantage of injection molding is repeatability. Molds can last for millions of parts with minimal wear. That is how the parts from one batch to the next to be almost identical. Each part with a CNC machine is put on the machine, and more variability.

David D. Hughes
Latest posts by David D. Hughes (see all)

Leave a Reply