How to reduce CNC machining costs?

May 5, 2024

Computer Numerical Control (CNC) machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. CNC machines come in many different forms with the most common being the 3-, 4- and 5-axis CNC machines. With each additional axis of freedom, the complexity of parts that can be produced increases. We shall explore these 3 types of CNC machines further in this article.

Before that, do check out our previous articles on CNC manufacturing listed below for a better understanding of the guidelines when designing parts for CNC machining.

Factorem’s ISO 2768 Machining Guidelines

Drafting technical drawings for CNC Fabrication

Dowel Pin Tolerance and Fit Standards

CNC Machining — Do you need 3/4/5 axis machining?

Introduction

Since the early 1900s, traditional manufacturing methods have been replaced with machines. Work which once required skilled labour to operate individual machines for each process such as the lathe, drill press, milling machine and more, can now be done with a single computer-programmable CNC machine. In CNC manufacturing, machines are operated via numerical control (NC), wherein a software program is designated to control an object.

Today, CNC machining is gaining popularity rapidly in the industry as more enterprises switch to an automated workflow by replacing manual labour with machines and humanoid robots. This has boosted the requirements for custom-made machined parts. However, these custom-works bring with them a different set of challenges that are unaccounted for by many companies until they are surfaced by machinists. We have compiled some of the most prevalent issues in this article to assist your considerations before approaching machine shops with your unique ideas.

Assumption made is that custom parts are parts which are unique and hence of low quantity. They may or may not necessarily be very complex.

Photo by Frank Hermers from FreeImages
Photo by Frank Hermers from FreeImages

1. Higher Set-up Costs

Logically, parts with lower order quantity (< 10 pieces) will cost more per piece as compared to orders of large volume. The main reason behind this is the initial set-up cost. All machine shops have a fixed rate not only to turn on their machines, but also for each set-up required in the machining process. Let us illustrate this with an example.

For example, a single part requiring machining on 2 separate faces would require 2 separate set-ups on a regular 3-axis CNC machine (the most common variant available). Assuming each set-up costs $40 and the switch-on cost is $40, for one single part, the total set-up cost itself would amount to $120. Now consider if the same part needs to be produced to a quantity of 10. The total cost for 2 set-ups and switching-on remains at $120 since each of the 10 blocks can be loaded in the same fixture in place for the very first part. Even if a handling fee of $10 is applied to each of the 10 parts, that would be a total set-up cost of $220 which is $22 per piece.

None of the prices in the example above are representative of market rates and are purely for explanation purposes. It can clearly be seen that if only a single part was to be made, the set-up cost would be almost 6 times more expensive per piece compared to a larger order of 10 such parts.

Lesson: Custom parts will inherently be expensive, and it is not uncommon for prices for less than 10 pieces to be more than double the prices that you anticipate based on past experiences with bulk orders.

2. Rising Material Prices

Covid-19 has had significant impacts on all of our lives and every industry in the world. The machining world has been hit hard as well with prices changing at times up to twice a week, never decreasing. One of if not the most important criterion for quotation is the price of the raw material required. With prices increasing dramatically every other week, this means that quotations are valid for a much shorter period of time. Additionally, material stock takes much longer to arrive with many backlog orders still yet to be cleared. This means that the base price for the same part is ever-changing.

Lesson: Most companies as well as government organisations require multiple quotations for comparison purposes, however, the decision needs to be made fast. Hesitate and it could cost you quite literally.

3. Standard Raw Material Sizes

Building on the previous point about rising material prices, raw material is also mass produced in certain standard dimensions. Shortages in supply chains for raw materials due to the pandemic as well as steep prices mean that your trusted supplier may no longer have the same standard metal tubes or metal sheets in stock.

Also, your supplier is likely to preserve whatever material he has to cater to larger orders. This is to minimise wastage as well as offer the best prices. Also, if your supplier may be unwilling to purchase stock material for your request if his available material is unable to suit your needs.

For example, if the machinist requires to buy a Steel tube which he does not otherwise keep in his storage, your one-piece requirement which is less than a quarter of the stock tube length does not make economical sense for him/her to take up the order. It would also be very expensive for you as you will have to bear the cost of the entire stock tube as there is no guarantee that material will ever be used by another customer or order ever again.

Lesson: There are a few ways to get around material related issues. The easiest being providing the stock material from your own expense. This will save your supplier on material cost and increase your chances of having your order accepted as the unused material no longer becomes a liability for your supplier. The other option is to remain flexible with regard to your part design. Have an open mind to changes in certain dimensions and material thickness so as that the supplier is able to make your part from the material that is already available on hand.

Conclusion

The current situation may be a historic anomaly, but its repercussions are here to stay. With supply chains adapting to streamline processes and adapt to just-in-time custom manufacturing, the resulting changes will continue to drive up manufacturing costs in general and specifically custom-manufacturing requirements for the foreseeable future. However, if you take notes of the points mentioned in this article, you will definitely save yourself shocking and unexpected results.

Thank you for reading!