Get It Right the First Time, Every Time.
A global market has changed manufacturing into a competition. The industry is dealing with a constant demand for shorter lead times, better quality and lower production costs. Every individual manufacturing process is a race to the finish line and at the end of that race, another one starts. A manufacturing pace of endless races can place a tremendous amount of pressures on machines, programmers, setup personnel and operators. They are like the driver and pit crew trying to capture first place in a race to produce quality parts with the least amount of costs. Being in an endless race your driver and pit crew need to be fully resourced.
Your winning formula always includes a well equipped programming staff. By investing a considerable amount of money on equipment and training for their programmers, companies have provided the necessary CAD/CAM resources to find the shortest cycle times in the race for production speed. Programmers have the advantage of CAD/CAM, but what edge are you giving your setup and operational staff? After all, they are your front line responsible for keeping your machine tool in the race.
Spend more time on the race track and less time in the pits
Unscheduled production stoppages to deal with machine and tooling issues can result in a lost race. When you are trying to keep a machine running for as many hours in the workday as possible, efficiency and preparation are the only ways to turn minutes of downtime into seconds. A lot has to happen behind the scenes before an operator can push the cycle start button on a machine. Additionally a lot more should also happen while the machine is running. In a typical shop, for an assortment of reasons, a lot more does not happen. The most common reason, “It worked the last time” can only get you by for so long before something goes wrong.
Delays are never part of someone’s race plan. So how do you empower your production and what resources do they need to reduce downtime during and between races? Attention to detail on all fronts will help you achieve ultimate production efficiency. The cost to address these details is minimal in comparison to the operational losses of a cell that is not running at peak performance.
These nonstop races are being run at ever-increasing speeds. As machine tools increase their cutting and, safety requirements also increase. These higher speeds require the entire complement of production components to be managed. The accuracy and rigidity of the machine tool spindle and tool holder assembly is critical as well as that of the work holding device and the work piece. Day to day racing can push your machine tools’ maintenance schedule to the limit and leave little time for the pit crew to manage other important aspects of your production cell. There is no better time to equip your production staff with the resources they need to keep your company in the race.Empower your production team with time and resources
After a program has been with CAD/CAM technology, a good production team can submit and pass a part through first article inspection after only one try. When given additional time and resources, your setup and operational staff will also be able to:
- Achieve a scrap rate of zero
- Optimize tool life
- Maintain machine tool health
Part of a company’s search for opportunities to cut cost must include a review of the cause of all unscheduled machine downtimes. By addressing the cause of these unscheduled stoppages, you will be able to implement a plan to keep everyone and everything operating continuously at peak performance. The investments are minimal and the extra time required by operational staff to execute these functions will be quickly recovered through a decrease in unscheduled production stoppages and an increase in quality.
All the metrics of preventative maintenance and life cycle management result in reductions in overall costs and increased reliability. They are absolutely necessary if companies want to meet all of their production deadlines and achieve the ultimate level in manufacturing, a scrape rate of zero. Managing the time consumption for these activities is crucial. If you are going to increase the responsibilities of your production team, you will need to make sure they are well trained and resourced.
Necessities or Accessories
Since machine tool performance does not normally degrade over short periods of time, many small occurrences will typically stack up to create an issue. Identifying the causes of these small occurrences, noting their effects and correcting them as soon as possible is critical to the long term health of your production equipment. Your production staff will also benefit, because when there are no failures, no one is responsible for failure.
What many consider machine tool accessories are actually necessities for companies that aspire to be the best. When you want to get it right the first time and every time after that, it is imperative that you pay proper attention to and manage variables that are not debugged by your CAD/CAM system. Specifically, attention should always be paid to the:
- Machine Spindle
- Tool Holder Assembly
- Machine Table Work Space
These unaddressed variables which are not sufficiently modeled during tool path verification can play havoc with form and positional tolerances, feature size and surface finish. Since your CAD/CAM systems will not be considering variables in machine spindle or tool holder run-out, cutter performance will always be an issue. Additionally the rigidity of the tool holder and workpiece are also critical to producing acceptable quality parts.
Manage your machine spindle
If it is possible for a company to cost-justify a new machine by projecting down time and lost productivity due to age, wear and abuse, it is also possible to cost-justify the care of an existing machine. You can extend the amount of time it takes before a machine is no longer able to be competitive by exercising due diligence when it comes to care and maintenance. Most companies follow manufacturer’s guidelines for machine maintenance; however these guidelines cannot insure that a machine will continue to perform as if it were new. An in-depth maintenance and care schedule is your best investment to keep a machine's tool in good operational condition and capable of producing quality parts.
Start with the CNC spindle as its condition directly affects the machine tools performance. Everyone around a machine should be encouraged to clean and check the spindle as often as possible. Your spindle management checklist should include inspection of the:
- Retention Knob Pull Force
- Amount of Dynamic Run-out
- Accuracy of Mating Surface
- Cleanliness of Mating Surface
The tools required to perform these functions are readily available. Since spindle rigidity and accuracy have a direct effect on the machine tool as a whole, it is a good idea to acquire a retention knob pull force gage for your spindles. Test the draw bar force on a regular basis. If draw bar force falls below a certain level, your tool life and surface finish will decrease. You can also damage your spindle and tool holders. Continual opeation of a machine with low draw bar force will allow the two mating surfaces of the tool holder and the spindle to rub. This lack of rigidity between the spindle and the tool holder may result in friction that will degrade the surfaces of your tool holder and spindle, thus leading to premature failure. This wear condition, which visually manifests itself on tool holders and spindles, is referred to as fretting.
It is also desirable to frequently check the dynamic run-out of your machine spindles using a precision gauge bar, a perfectly concentric steel cylinder that measures the spindle rotation against its centerline. Lower spindle run-outs will yield an increase in machine tool performance, extend tool life and most importantly, extended your spindle’s life. Visual inspection and gauges should be used to check the spindle geometry. Excessive spindle wear can only be corrected by regrinding, so take control of your machine tool’s spindle.
Since machine tool run-out stems from wear of the spindle bearings or the ground spindle geometry, these are important checks. To operate correctly, machine spindles must also be kept clean. Any particles or contaminants that gather between the two mating surfaces will cause the surfaces to wear away, weakening the fit and severely impacting machine accuracy. Using spindle cleaners several times a day to wipe clean the spindles’ contact surfaces will improve precision and prolong the life of the machine tool as well as the cutting tools and tool holders that go into the spindle. Special tool holders are also available that use the coolant feature of the machine spindle to clean the spindle face automatically. All of these procedures can be worked into the day-to-day operations of your machine tool with minimal or no negative impact to your current production capacity.
Manage your tool holder assembly
The relationship of the tool to the tool holder is just as important as the relationship of the tool holder to the spindle. Unlike spindles, which operate within the controlled environment of the machine, tool holders can be exposed to many pollutants all around the shop. During storage and between uses, tool holders run a high risk of picking up oils, dust and other particles that can contaminate their surfaces. Cleaning the exterior of your tool holders is an important step before placing them into your tool-changer or spindle.
Before loading a cutting tool into a machine, several factors may need to be qualified. The process of assembling a tool can introduce variables such as:
- Run-out
- Balance
- Size
- Rigidity
In order to control these variables, it is best to have clean components that are geometrically correct. The tool holder is designed to hold the tool with sufficient clamping force to overcome the forces of the cutting operation. It also must deliver the tool to the spindle centerline. Both of these functions can be degraded by many forms of contamination. Reductions in gripping strength and deviations from centerline will lower tool performance, so cleanliness is critical to achieving maximum tool life and material removal rates.
All tool holders have a better chance of delivering the tool to the proper location and holding them firmly when components are clean and free of contamination. Complex tool holders such as collet chucks should be completely disassembled and cleaned between uses. Wipers are available to clean the internal surfaces of the collet body and the spring collet should have contamination removed with cleaning systems such as ultrasonic or high-pressure washers.
Once all components have been cleaned, tool holder assembly can begin. The tool holder should be protected while it is being assembled and disassembled to keep from damaging surfaces. Tool assembly devices are available to assist in safely gripping tool holders. Avoid serrated grippers or loose fits which can easily scar tools and tool holder shanks. When tools and holders are required to rotate at high speeds, it is critical that their original surfaces are preserved.
When spindle speeds require a balanced tool, there are two approaches to delivering a qualified tool to the spindle. The first approach uses precise and balanced components. If everything is clean and in proper operating condition, components can be assembled and sent directly to the machine tool. If the tool holder components and cutting tool are manufactured to a lower level of precision, they can be assembled, balanced offline and then transferred to the machine tool.
Offline tool presetters are excellent tools to find and remove run-out from tool assembles outside of the machine spindle. They are also the best way to set tools to specific sizes. As a measuring and inspection device, tool presetters can inspect and measure all forms of geometry associated with today’s most complex cutting tools. In lieu of offline presetting, probing systems can be installed in the machines to measure and monitor tool lengths.Manage your machine workspace
Workpiece handling needs to be treated the same way as tool holder assemblies. If you need a large number of tools available on-demand to meet all of your production needs, you expand your tool-changer or quickly swap out tool holder assemblies in the carousel. Consequently, if you need a large number of workholding devices to produce all of your products, you will need to swap out workholding devices or add machine tables.
Duplicating machine tables requires large amounts of floor space and is usually cost prohibitive. Pallet pools on horizontal machining centers have proven to be the exception to this rule. For companies that cannot duplicate machine tables, it is desirable to have the workpiece handling system positioned and clamped in a way that would allow the production process to commence without having to indicate it in the handling device. Most companies choose to retrofit a quick change positioning and clamping system to their machine table to facilitate these changeovers. These workholding systems need to provide fast, accurate and rigid positioning and clamping. The most common quick changing machine table setup systems are:
- Grid plates
- Zero-point clamping systems
- Shuttle tables (for vertical machining centers)
Grid plates provide a repetitive series of accurate bushing locations that accept positioning pins to locate workholding devices or workpieces. These positioning locations are intermixed with threaded locations which provide a means of attaching clamps to hold the workpiece or workholding device with sufficient rigidity for the production process.
Zero-point clamping systems combine positioning and clamping into a single process. A retention knob with a geometric reference datum is appended to the workholding device or workpiece. The clamping process draws the retention knob into a ground reference which allows for simultaneous positioning and clamping. Small workspaces can be addressed with a single retention location. Larger components are addressed with multiple clamping locations.
Shuttle tables consist of a track mechanism that connects the machine table through a rail system to a table storage position. One workholding table can be shuttled out of the machine and a second table can be shuttled into the machine.
Are you in the race or temporally stalled in the pits?
CNC machine tool efficiency is all about managing the components that need to come together in proper alignment. Your operational staff already has the skill set to implement a management procedure for the machine spindle, tool holder assembly and workspace, while your programming department links all of the pieces together. All you have to do is provide the resources and turn over responsibilities to your employees to deliver production uptime and quality.
