Maintaining Productivity with Repeat Business

Decisions made in your CNC environment must reflect your company’s needs, and to make wise decisions, you must understand factors that contribute to your company’s identity. The most important factor is company type, which I have addressed in previous columns.

What types of companies use CNC machine tools?

To review, here are the four types of companies that use CNC machine tools:

1. Product-producing companies. Revenue comes from the sale of products.
2. Workpiece-producing companies (job/contract shops). Revenue comes from the sale of component workpieces to product-producing companies.
3. Tooling-producing companies. Revenue comes from the sale of support tooling (fixtures, gages, cutting tools) to product- and workpiece-producing companies.
4. Prototype producing companies. Revenue comes from the sale of prototypes to product-producing companies.

Some important generalizations can be made based on company type alone, including shops’ tendencies to repeatedly run the same jobs on their CNC machines and how often they run these repeat jobs. The more often a job is run/repeated, the easier it is to justify costs associated with making improvements.

Product-producing companies tend to have the most repeated jobs. Indeed, these companies tend to run the same jobs over and over. In addition, it is not unusual for product-producing companies to have lengthy and predictable lead times, meaning they often schedule jobs to run on CNC machines well in advance. For example, a quantity of 500 of a given workpiece may be required in the assembly department every month; the schedule is made accordingly. Everyone who works in this kind of CNC environment knows the schedule and can prepare for upcoming times when the job will be run.

With lots of predictable repeat business, it is imperative that a shop streamline or even eliminate repeated tasks. Its focus must be on minimizing machine idle time, both during setups and production runs. Developing qualified workholding setups, for example, can eliminate time-consuming tasks related to program-zero assignment. Ensuring that cutting tools remain intact from the time one job is run to the next will eliminate the need to reassemble them.

When tasks cannot be eliminated, a shop must find ways to perform them offline, in preparation for upcoming jobs, while machines are in production running other jobs. Kitting components is a great example. With everything needed to complete the job at hand, the CNC machines will not sit idle waiting for operators to find needed components.

If your shop cannot justify what it takes to eliminate tasks or move them offline, your last alternative is to “facilitate” them. That is, make them as quick and easy to perform as possible. If the tasks of (manual) workpiece loading and unloading, for example, cannot be eliminated or moved offline, find ways to help operators perform these tasks. While watching them, you may find room for improvement. 

You may find, for instance, that operators are cleaning and deburring, maybe even inspecting, the completed workpiece before they load the next piece of raw material. Make sure they know the importance of keeping these tasks internal to the machining cycle (which in turn, moves them offline).

Workpiece-, prototype- and tooling-producing companies tend to have less repeat business. Some jobs may end up being repeated jobs, but these shops may not know at the time an order is placed whether the job will ever be repeated. And of course, there will be no way to predict when the job might be run again. In this case, it does not make sense to put too much effort into eliminating or moving offline any tasks that are specific to a single given job.

With limited repeat business and unpredictable lead times, you must concentrate on tasks that are common among the jobs you run. While you should look first for tasks that can be eliminated or moved offline, finding them may be more difficult and harder to justify. For example, it will not be feasible to keep cutting tools assembled for a given job, since the job may never be repeated. But it will make sense to keep the most commonly used cutting tools assembled and placed near/in the CNC machine that uses them. This eliminates the need to reassemble them when they are required.

Most improvements you make will probably fall into the category of facilitating tasks. Use frequency and difficulty levels to set priorities. Target first those tasks that are difficult and often-performed. A simple suggestion is to look for times when people struggle, and then provide some help. 

You may find, for example, that operators struggle when making sizing adjustments. The required measurements, calculations and offset adjustments may be resulting in scrap-causing mistakes. Or you may feel the related tasks are taking too long. There are many ways to simplify these tasks, including better documentation that specifies tolerance limits and connecting cutting tool station numbers to machined surfaces on the workpiece.