At the start of early childhood, we learn the importance of safety. From taking the time to buckle your seat belt to following the appropriate safety precautions during a fire drill, we acknowledge that even though we may not want to make these steps, they are still necessary. Preparing and practicing such steps allows for safety to become routine. That means that when something does go wrong, you are well prepped and ready for action. Safety is a guiding principle throughout our entire lifetimes. As we reach adulthood, we continue to prepare for the unexpected. Proper safety precautions become especially important when operating dangerous equipment like CNC machines. Whether you are a beginner or a skilled operator, taking precautionary actions is crucial.

Computer-Generated or Manually Programmed: Precaution is Always Necessary

Dealing with industrial equipment can put operators into dangerous situations. Whether you are a novice or a seasoned machinist, precautionary steps are critical to a safe and successful experience. Manually programmed machinery often has complications. A misplaced keystroke or inaccurate digit may cause an error. Even a small error of this nature can cause an entire job to be scrapped and put the operator at risk of injury, making safety measures that much more critical to the machining process. 

Flaws may even be found in computer-aided manufacturing (CAM) systems. Although they are more likely to be correctly constructed, issues like incorrect feed, speed, or workholding can occur. For this reason, safety precautions are applied to CAM systems as well. Despite, the reduced risk for complications of the CAM systems, safety protocols should always be followed to protect the operator.

 

The Top Three Priorities 

Working with any CNC machinery requires safety measures. No matter how much experience an individual has acquired, there is never a point where one “outgrows” precautionary steps. These safety tips can be divided into three levels. 

  1. The Operator – Even if the person operating the machine is an experienced professional, safety precautions are still necessary. It is common for an individual to cut out safety steps because they feel that their skill and experience will compensate. Despite this appeal to efficiency, the increased risk is not justified by the saved time. 
  2. Machine Tools – CNC equipment is expensive and often difficult to replace. Taking the proper preventative measures can prevent the expenses that accompany new parts or buying an entirely new machine. Repairs and machine replacement along with lost productivity can create a large price tag. Well planned safety protocols protect the machinery as well as the operator.
  3. The Workpiece – Depending on the materials used, incorrectly machining pieces can become extremely costly. Expenses may range from ten cents per piece to several hundred dollars of scrapped material. For this reason, the company must ensure that their operators are taking the essential safety steps to prevent extensive loss of profits and guarantee the workpieces are correctly made at the appropriate size during the first production run.

The Steps that Save

To avoid some typical mistakes that come with CNC machining, the following steps should be taken to verify programs:

Recognizing Flaws in Syntax

If your CNC machine has a switch labeled machine lock, this procedure can be used to scan the entered program for syntax mistakes. When the program is setup up, the machine lock is turned on, and the switches are dry run. By turning up the dry run motion switch the control moves through the program quickly, scanning for syntax mistakes. If a mistake is discovered, the alarm will sound and notify the operator of an error. The operator must then identify and make the required changes, running it through the machine lock dry run again. This process is repeated until the program cycles without sounding the alarm. 

Identifying Motion Issues

After the syntax of the program is approved, the motion of the program is tested. Particular care is required by the operator, especially since there is no workpiece in place.  To complete this procedure the operator must:

  • Turn off the machine lock switch
  • Decrease the dry run motion rate as much as possible
  • Put the rapid override switch to its lowest setting
  • Be ready to press the feed hold button

The motion of the program is studied by the operator to ensure it flows correctly. From there the jog feed rate can be adjusted to a comfortable speed. If there seems to be a flaw the operator can stop the cycle by pressing the feed hold button and then the reset key. After stopping the cycle, the operator goes back and makes the necessary adjustments. 

In addition to examining the machine for serious motion issues, the operator should also check for proper spindle rotation and other necessary program motions. In order to ensure there is an accurate evaluation, this process should be run several times to allow the operator to catch all major and minor issues.

Confirmation of Drill Motions

The operator should complete a cycle with the dry run switch off, without using a workpiece. In the prior procedure, the operator was able to take control of the motion rates with the dry run motion rate switch. However, with this switch on, the operator is not able to spot the difference between rapid motions and cutting motions. This can cause issues like drills working at rapid where they shouldn’t be, potentially causing a broken drill or even an injury. By completing this final check of the cycle without a workpiece, the operator can ensure the drill is rapiding in the program where it is needed.

Applying the First Workpiece

Rapiding a tool within 0.100 inches of a workpiece is common among programmers and impossible to verify with the prior procedures. For this reason, the operator must be cautious with the first application of a piece. We recommend that the dry run and the single block are turned on during each tool’s approach to the piece and during rapid motions when relocating to new surfaces. By turning these on, the operator will be able to control the motion rate during the tool’s approach. The single block ensures that the clearance approach amount is adequate. Once everything is in line, the operator may turn off the dry run switch, leaving the single block switch. When a command is complete, the motion stops and the operator must press the cycle start button to move to the next command. If the successive motion is a rapid movement the dry run can be applied to control of the motion rate. The operator can also use the feed hold button and the position display to make sure the machine stops before it hits the workpiece. This feature is commonly called the distance to go page, and it allows the operator to see how much further a motion will go until the machine stops. 

Optimizing the Process

After the first product of the machining process is complete, the process needs to be optimized. Optimization allows for maximum efficiency during the production period. We recommend that the machine does not rapid for the first few pieces to enable the operator to get comfortable with the cycle before speeding it up. This precaution allows the operator to evaluate the process more efficiently and minimizes the cycle time where it is optimal. If there are any significant program changes, we advise that you go through the verification process again. 

Learning to Expect the Unexpected

Despite what may seem like a lengthy list of procedures, going through the verification process for each of your programs allows you to maximize efficiency. The verification process protects the safety of machinists and prevents unnecessary wear and damage to the machinery saving money in the production process. As with any safety precaution, it is meant to assist you in situations when the unexpected occurs. When it comes to safety, there is no time limit!

Sources

https://www.mmsonline.com/articles/key-cnc-concept-10verifying-cnc-programs-safely

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