Programming Dull Tool Replacement

Columns From: Modern Machine Shop,

Posted on: 2/18/2013

This custom macro will provide consistency to the process and help you control tooling costs.

Editor's Commentary

From the monthly column: CNC Tech Talk

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Mike Lynch

With long production runs that require many workpieces to be machined, dull tools must be replaced in a timely manner. If they are replaced too soon, your cutting tool costs will be higher than they should be. If they are replaced too late, you run the risk of catastrophic tool failure that will result in a scrap workpiece, a damaged cutting tool and possibly a damaged machine—and time will be wasted while people scramble to get the machine up and running again.

Since catastrophic tool failure can be, by far, the more costly of the two scenarios, most companies err on the side of caution. They wisely strive to replace cutting tools well before they are completely dull.

There are many companies that leave it completely up to the CNC operator to determine when a cutting tool is dull and in need of replacement. And if the company has several operators involved with the job (possibly multiple shifts), it is unlikely that there is any consistency related to when dull tools are replaced. Indeed, many operators get in the habit of replacing all cutting tools (or indexing/replacing inserts) at the beginning of their shifts, regardless of when the cutting tools were last changed.

If you study the tool cycle for an extended period of time, you can actually program replacement of dull tools. That is, you can create a program to monitor the number of workpieces being machined by each tool, generate an alarm and make the machine stop when a tool must
be replaced. This will eliminate inconsistencies among operators, enable you to set dull-tool replacement intervals that are safe and give you more control of your tooling costs.

The program below requires custom macro B. It is set up for six tools but can be easily modified to accommodate any number of tools.

Of course, to use it you must know how long each tool will last. Once you have this information, set common variables #101 through #106 to the number of workpieces that can be safely machined by tools one through six. Insert the machining program commands after the series of tests. Be sure the values of permanent common variables #501 through #506 begin at zero. (You can see/set them on the variables display screen page.)

O1000(Tool life monitor within machining program)

(SET TOOL LIFE VALUES FOR TOOLS 1–6)
#101 = 100 (Tool life value for T1)
#102 = 150 (Tool life value for T2)
#103 = 150 (Tool life value for T3)
#104 = 200 (Tool life value for T4)
#105 = 250 (Tool life value for T5)
#106 = 75 (Tool life value for T6)

(Tests for dull tools)
IF [#501GE#101] GO TO 1000
IF [#502GE#102] GO TO 2000
IF [#503GE#103] GO TO 3000
IF [#504GE#104] GO TO 5000
IF [#505GE#105] GO TO 6000
IF [#506GE#106] GO TO 8000

(MACHINING COMMANDS GO HERE)

(Counters)
#501 = #501+1
#502 = #502+1
#503 = #503+1
#504 = #504+1
#505 = #505+1
#506 = #506+1
GO TO 9999

(Alarms to stop machine with messages)

N1000#501 = 0 (Reset life count for T1)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T1)
GO TO 9999 (Skips over alarms and goes to M30 code)

N2000#502 = 0 (Reset life count for T2)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T2)
GO TO 9999 (Skips over alarms and goes to M30 code)

N3000#503 = 0 (Reset life count for T3)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T3)
GO TO 9999 (Skips over alarms and goes to M30 code)

N5000#504 = 0 (Reset life count for T4)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T4)
GO TO 9999 (Skips over alarms and goes to M30 code)

N6000#505 = 0 (Reset life count for T5)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T5)
GO TO 9999 (Skips over alarms and goes to M30 code)

N8000#506 = 0 (Reset life count for T6)
#3000 = 1 (TOOL LIFE OVER CHANGE TOOL T6)
GO TO 9999 (Skips over alarms and goes to M30 code)

N9999M30

This should give you a consistent tool-replacement program that is safe and cost efficient. 

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