Machine Warm-up Routine - Why? When? How?

As former field service engineers ... one of the items we always stressed to our CNC customers was the importance of performing a machine warm-up routine. Below are answers to some of their most frequently asked questions ... which pretty much tell the whole tale about this activity.

WHY?
A machine warm-up routine benefits both the machine and the machining in a number of areas :

• Running the spindle and moving the axis give the oils in the machine ... spindle oil and way lube ... an opportunity to distribute and do their jobs. Especially in a colder environment ... start of the day when perhaps the heat in the shop was reduced for the night ... running the spindle and moving the axis gives the oils a chance to warm up to their appropriate temperature and "work" the way they were intended. The end result is improved machine life, operation and reduced down time due to break downs.
• It stands to reason also that when the oils are working as they were intended ... the accuracy of the machine can more easily be maintained. It is an unreal expectation to assume that you can walk in in the morning and start the machining and hold a tolerance of .0005" ... perhaps when the machine is brand new ... but not in the "real world". Starting your day like this will most likely result in offset adjustments being made due to the machine's "cold" condition ... and will begin the process of "chasing" size for quite a while. I heard countless times from customers how they spend 1-2 hours in the morning "chasing" size. Hello? Did you warm up the machine?

WHEN?
A lot of people assume that performing a machine warm-up routine is only appropriate after an extended "vacation" period ... either by the personnel or by lack of work flowing to the machine. While a longer warm-up period is recommended after an extended break ... an everyday warm-up routine is still recommended for the reasons listed above. Here are a couple of options for when to perform a machine warm-up routine :

• Start of the Day ... whether that's at the shop opening or the start of the 1st shift.
• After the machine has been idle for a time period of over 4 hours.
• After an extended vacation period.
• If the shop temperature is cold during the winter months ... a short warm-up should be performed even after lunch  / dinner breaks.
• If the machining requires holding a tight tolerance ... a warm-up routine should be left executing during ANY breaks in the machining ... inspection time, bathroom break, at machine deburring process, etc..

HOW?
Matching the situations above requires an assortment of warm-up routines. No matter what the length of time ... the warm-up routine should always include the following :

• Spindle running
• Axis moving along the full stroke of each axis.

The beauty part is that the various warm-up programs can be left in the CNC control and called up anytime as needed. Or in the case of just keeping the spindle warm ... it may be a case of just manually starting the spindle and leaving it running while you walk away and attend to something else.

Spindle Warm-Up
After an extended break the spindle should be run through all the speed ranges with substantial dwell times in between speed changes. Start slow and work your way up with at least 15-30 minutes between increases. An example of a Fanuc style program might be :

• G97 S100 M03
• G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
• S300 
• G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
• S500
• G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
• etc. etc. etc. until a speed of at least 3500 RPM is obtained.

You can create a program like the above to be run after extended breaks ... and a program with less dwell time to be run after shorter breaks.

As mentioned above ... to maintain the spindle temperature during the course of the workday ... manually starting the spindle at say 2500 RPM and leaving it running while you leave the machine can also be quite beneficial in maintaining machining accuracy.

Axis Warm-Up
After an extended break  ALL the machine axis should be made traverse the complete length of each axis ... or if fixturing / workpieces are in the way the maximum length of the stroke that is possible ... using various speeds. You don't want to start the movement under full rapid traverse speeds ... but rather work your way up during the warm-up cycle. The easiest way to accomplish this is to utilize the RAPID OVERRIDE feature on the machine. The G code warm-up program will call for G00 / rapid ... but start the program with the RAPID OVERRIDE switch at it's lowest percentage .... then work it up manually as the routine runs. A sample Fanuc style axis warm-up program might look like this :

• G00G91G28Z0
• G00G91G28X0Y0
• G00G91Z- ***** .... incrementally move the Z axis as close to the table as possible.
• G00G91G28Z0
• G00G91X ***** .... incrementally move the X axis to the opposite end of it's stroke
• G00G91Y ***** .... incrementally move the Y axis to the opposite end of it's stroke
• G00G91G28X0 ...... move the X axis back to the zero return / home position
• G00G91G28Y0 ...... move the Y axis back to the zero return / home position
• G00G91X ***** Y ***** .... incrementally move both axis at the same time to their stroke end
• G00G91G28X0Y0 .... move X and Y back to their zero return / home position.

The above routine gives you an idea ... and feel free to make additions as you see fit. The main idea is to move ALL the axis along as much of their stroke as possible. Not just a "square" pattern ... try to make "fancy" moves that can move all the axis through as much of the strokes as possible.

If you don't like or don't have a RAPID OVERRIDE option ... you can simple make a longer program using FAST feedrates ... such as :

• G00G91X ***** F100.00
• etc.
• etc.
• G00G91 X**** F200.00

You can get the idea ... repeat the program and alter the feedrates as the program progresses. Again ... the good part is that once it is written, you can maintain the program in the machines memory and recall it as needed. No need to re-create it each time.

Spending some time creating these warm-up routine programs ... and instituting a policy of when and how they are to be run ... can go a long way to improving your machine's life ... as well as your machining efficiency and accuracy.

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Happy Chip Making ... and may you Make Chips and Prosper !!

Your Way Lube System - Friend or Foe ?

Your CNC machine is equipped with an automatic oiler system. Great ! You won't have to think about oiling the machine and an alarm will tell you when the tank is dry. What a great device ? Right ?

Well, that is the design. Unfortunately, along with the "automatic" description of the system comes the "out of sight, out of mind" aspect of the system. Because many people know it is an automatic system, many people put it out of their minds and simply wait for the alarm to come up showing that the tank is empty and needs to be filled. But what if that alarm never comes on because the tank isn't empty ? Why wouldn't the tank be empty ?

As your machine gets older, the way lube system will require service just like any other mechanism. The main problem, which often gets overlooked, is that the "tank empty" alarm never comes on because the tank never drains and nobody ever notices it. Now your machine runs for months on end with no lubrication on the ways and when you finally notice a problem, it's too late. Here is the "Rest of the Story ..."

PROBLEM :  The machine's ways are not receiving any way lube oil.

SYMPTOMS - IN ORDER OF SEVERITY :

• Positioning / Repeatability Problems
• Axis makes noise when moving
• Axis Drive motor overload alarm coming when the axis is moving

POSSIBLE CAUSES :

• Way Lube Pump burned out.
• Way Lube Pump distribution flow set too low.
• Way Lube Pump filter CLOGGED
• Way Lube line BROKEN
• Metering Units are CLOGGED

POSSIBLE CAUSES EXPLAINED :

(1) Way Lube Pump Burned Out : If the way lube pump is burned out, obviously there will not be any lube getting into the system. These pumps are usually set using a timer system. There is basically two types of timer systems used :

• The pump is on a cam and the way it works is that the pump is always running. One gear turns another which acts like a step-down system and the second gear raises a "primer" lever. When the lever reaches the top of the stroke, the "primer" lever is released and the oil is pushed into the lines. This whole cycle can take 5-20 minutes meaning that even though the pump is always running, the lines get lube only every 5-20 minutes.
• How to Check It : Take a flashlight and look in the tank or remove the oil tank. Once looking inside, you can see the main gear that should be constantly moving. It may be at a very slow pace, but you will see it moving.

• The pump is set to an electrical timer set in the controls PC (programmable controller) or an actual physical electrical timer in the cabinet. This type of timer only supplies power to start the pump for every cycle.
• How to Check It : On some pumps there is no primer lever but a light comes on on the tank when the pump is activated. Make sure this light comes on every 5-20 minutes or some other sign comes on to show the pump is activated every 5-20 minutes.

(2) Way Lube Pump distribution flow set too low : As stated above, the way lube pump usually is set using a timer system. The flow amount that gets distributed into the lines during every cycle is usually set and adjusted at the pump with a manual setting mechanism. This type of adjusting mechanism is usually a knob that can be turned higher or lower to set more or less flow. Also, just look at the primer lever. During the mentioned 5-20 minute cycle, you should see the primer lever raise slowly and then start to drop after reaching the top of the cycle. Check the stroke of the lever - short stroke, less flow.

• How to Check It : The normal pump usage is in an 8 hour shift, you should fill the tank every 2-3 days. Also, you should see way lube flowing onto the ways. Always remember, the more flow the better. Yes, it may contaminate the coolant but that is better than ruining the ways and thus the machine just to save a couple of bucks.

The photo above shows a way lube pump unit which includes a manual flow control device. Adjusting the white knob adjusts the amount of lube being distributed per one cycle of the lube pump. When this type of pump is working correctly, you can see the white knob rising slowly then retracting, pushing the lube into the lines. The amount of rise and fall, and therefore the amount of lube distributed, is determined by the flow adjustment.

(3) Way Lube Pump filter CLOGGED : The way lube tank usually has a filter between the tank itself and the oil line that starts the distribution. This filter is usually in the tank itself at the bottom of the primer lever or in-line right after the main distribution line leaves the tank. It will get clogged over time, especially if there is no filter at the oil fill hole or if someone takes off the filter when filling the tank.

• How to Check It : Disconnect the main lube line where it exits the tank to feed the system or after the in-line filter if so equipped. When the cycle reaches the pump stage as outlined above, oil should flow through this connection. The flow should be strong at this point. If not, remove the oil tank and search out the filter or remove the in-line filter. They can often be cleaned with a cleaner but the best remedy is to replace it.

(4) Way Lube line BROKEN : Oftentimes a lube line in the system gets crimped or broken during machining or during service. These way lube systems are usually "pressurized" so to speak and if the pressure is released at one point, say at the broken line, the oil will flow all to that point, depriving all the other lines of fluid.

• How to Check It : When the pump is in the pumping stage, the primer lever should fall slowly. This is due to the fact that it is pushing the oil into the system. If a line is broken, the primer lever will fall quickly as all oil is funneled to the broken line area only. On systems without a primer lever, the pump may have a pressure gauge on the pump. During the pumping cycle, the pressure should register for a couple of seconds as the oil is pumped into the lines. If the pressure is low or does not come up at all during the pumping cycle, a line in the system may be broken.

(5) Metering Units are CLOGGED : In order to create the "pressure" of the system needed for even distribution, each oil line leads to a "metering unit" where the flow is lowered and the oil is discharged. When the pump forces oil into the lines, they all fill and flow to the metering units where the flow is stopped. Each metering unit is set to discharge the desired amount or "drops" of oil and perform their individual duties. Since some areas require more lube, the metering units can be different for each line or area. Since these metering units have actual valve type components in their very small bodies, over time these units can be become clogged or the inner workings can become stuck.

• How to Check It : This is a much harder area to check. The best remedy and prevention is to change these units every year as part of a yearly maintenance program. Because these units allow only drops to flow through, they are harder to see when troubleshooting. These metering units are usually located in "clumps" around the machine. Several lines lead to these central areas and lube lines are branched out from here to the various areas of the machine. Replacement metering valves should be obtained from the machine tool builder or dealer to insure that you are getting the correct replacement part. When changing these units, pay close attention to the flow arrow that is commonly marked on the units themselves. This arrow shows the direction of installation and flow. Check the original unit before removal and replace accordingly.

The photo above shows an example of some metering units. These individual fittings are usually located in one or two main terminal blocks that feed certain areas of the machine such as the axis and ball screws. As the system fills with pressure and lube, these fittings discharge the lube at their pre-set flow rate into their lube lines. Over time, like cholesterol in the arteries, these units become clogged and no longer allow lube to exit and thus deny vital areas of the machine the way lube they require. As part of a yearly maintenance program, metering units in the machine should be replaced as a precautionary measure.

Due diligence and a little tracking will 

insure your Happy ( and ACCURATE ) Chip Making

 for years to come !!

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