Beginner’s Guide to Production Machining

CNC machining is a process used in manufacturing to shape raw materials into parts with specific geometries, dimensions, and tolerances by removing material to obtain a shape or part. The difference between standard CNC machining and production machining comes down to volume of parts to be manufactured. Production machining focuses on repeatability and accuracy of tolerances, simply put part 1 must be identical to part number 5000. There is low volume CNC machining and high-volume CNC production machining.

Outsourcing production machining for a company can reduce overall costs and improve the quality and consistency of the parts being made. We recently spoke with Dean Sonquist, the owner of Plas-Tech Tooling to learn more about what companies should know about production machining and how to reduce time and costs as well as improve the quality of the machined parts.

 

What can affect machining pricing?

Lead times, raw material availability and tolerances all affect pricing.

Machining tolerance is a common factor that affects pricing.  At times buyers or engineers don’t always understand that a three or four place dimension may not be necessary for the part they are working on.   For example, some parts only require a saw cut compared with a significantly tighter tolerance that would require machining or even grinding. This is a big deal when it comes to the final cost of the part.

We review customer prints and ask questions regarding what does and does not matter?  Many times we hear, “well, my software was set up for three decimal place precision, so I didn't change it.”   This may seem like it is not big deal, but it can drastically affect the cost of the process.  So, using reference numbers or stating saw cut or mill surface is fine.   It is important to identify surfaces or features that are critical to your part and validate what needs the high tolerances.   If it doesn't require the tolerance, don't be as specific about it.  Your CAD software is an important tool, but remember you can adjust the final tolerance requirements for the part.

 

Have a Conversation with your Provider

Take the time at the beginning of your project to speak with your CNC machining provider. Tell them what features are critical, and discuss which tolerances are critical.  When possible, describe or demonstrate the application of the part.  This may lead to an ongoing dialog about the part.   Have a two-way conversation instead of blindly sending an RFQ and a print. The more questions that are asked, the more likely you are to have a part which better fits your needs and budget.

 

Material Call Outs

Using the correct material call outs will help reduce costs.   We often see prints requiring specific alloys like a 4140 called out, when a simple 1018 or 1045 would work just well.   Calling out the correct material can reduce costs and turnaround time.

 

Understanding Quantity and Volume

Regardless of volume or quantity, there are things that need to be done before production begins.

If you only need one part, your full setup cost is associated with that one piece.   If you need a hundred or a thousand pieces, the setup cost is spread out over more parts, making the cost per part more economically correct.  Some companies don’t understand the time and cost associated making only one part.

In addition to the setup, fixturing and tooling costs are all fixed costs that will get figured into a job. These costs are a constant regardless of the number of parts produced. The easiest way to reduce cost is by adding volume and trying to order all parts at one time or have purchase agreements for a higher quantity over time. This will spread the fixed costs over more parts and ultimately bring down your per piece price. 

We would also suggest thinking about part designs that can use the same part in different locations, like left and right-side parts.  Something like this may allow you to double the volume of a single part.

Before investing in a tooling fixture, you may want to consider rapid prototyping or machining one part to make sure it is exactly what you want.   Once you have hard tooling or the fixturing in place, you don’t want to find out you need to change the design for something you didn't think about and start all over again.  Proving out your concept and design in the beginning before you move towards the higher production run is one of the main things that needs to be thought about.

 

Finally, once you are committed to higher volume production, make sure there are quality standards such as gauging and measuring the parts in place. You don't want to use a manufacturer that has no plan for quality oversight.  Using a company with ISO 9001 or similar certification, can give you the piece of mind that your parts will be made right and function to your expectation. 

 

Many thanks to Dean Sonquist, owner of Plas-Tech Tooling, for sharing his insights on production machining.

Plas-Tech Tooling : www.plastechtooling.com