Feature Article - How to Achieve Intelligent Tool Management

FEATUREARTICLE

How to Achieve Intelligent Tool Management

With an effective tooling database, moldmakers can manage and track the information that is essential to their business.

By Randy Harper

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For more information contact Randy Harper of CAMM/Creative Advanced Machining Methods (Quincy, OH) at (937) 585-3483 or via e-mail at rharper@woh.rr.com.

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A tooling database that lets you intelligently manage your tooling and track both geometric and dynamic tooling information is essential to high-speed and conventional machining efficiency.

When searching for a tooling database that best fits your business, consider one developed in Access for WindowsT, which is both user-friendly and customizable - one that allows the user to easily view all of the dynamic information about a cutter assembly on its own full-screen, personal record. The user can then search for the best tools using any of the input parameters and produce reports for preset personnel, machine tool operators, NC-programmers or process engineers which help them to best utilize the tooling inventory for chatter-free rpm and maximum depth of cut.

Key Features of a Tooling Database
A tooling database should:

Allow input of all usual tooling geometry, diameter, gage length, allowable chip loads, SFM, insert type, manufacturer, grind geometry, etc.
Provide entries for balancing information, static and couple.
Compute maximum unbalance forces and cutting force loads for intelligent comparison of unbalance forces to cutting forces.
Allow for the tracking of tool dynamic flexibility and natural frequency while providing the best, chatter-free spindle speed and limit depth-of-cut estimates.
Track actual data of all tool setups.
Provide unlimited record storage capabilities (up to one million records).
Search for a desired tool characteristic - speed, diameter, etc. - or make predictions for future tool performance based on existing tooling data.

Evaluation of Necessary Tool Balance
High-speed machining re-quires better balancing of tooling. However, a consistent means of specifying required balance has yet to be properly standardized. A tooling database can address this problem by computing the unbalanced force on the cutter - based on balance machine measurements and the anticipated maximum cutting force due to chip removal. The user can then make a judgement as to the level of required balance by comparing these two values.

BALANCE MACHINE
A balance machine is highly recommended for high-speed machining. It's an excellent tool for inspection or quality control. The customer must choose his/her machine according to product support, capacity of minimum and maximum toolholder weight limitations which deal with sensitivity, adaptive tooling availability - such as HSK adapters, Cat or any other required interface - and single- or two-plane capabilities. A balance machine measures the force of unbalance during the rotation of the tool assembly and those forces are calculated within millionths of an inch of center of gravity. Some balance machines are more sensitive, while others are less sensitive, allowing for a range of capacity of the toolholders used. A tooling database gives the true numbers required to compare for intelligent decisions on balance issues.

Assuming that maximum cutting loads are better defined by power and torque limits of the spindle and tool, the user can utilize these values to provide guidelines for the required tool balance. For instance, if the tool balance is producing a 20-pound unbalance force, but the roughing cut is expected to generate a 200-pound peak cutting force, then the unbalance force will likely not produce any significant effects to the cut and no further balancing would be required. However, if the same balance force is computed for a finishing cut producing only 40 pounds of peak cutting force, then improving tool balance may be required to eliminate any detrimental effects - poor surface finish or accuracy, reduced tool life, etc. - from tool unbalance. The relative level of tool unbalance to peak cutting force can be specified by the user based on their experience and machining quality requirements - unbalance/cutting force = five percent, 10 percent, etc.

CUTTERS AND HIGH-SPEED MACHINING
Almost any cutter can be used for high-speed machining, but some are better than others. The problem is that the cutter is not the only deciding factor. Chances are that a certain cutter assembly may work differently from one machine tool to another unless they are similar in manufacture design such as the matching models, etc. Successful high-speed machining depends upon the material, balance, overhang, pocketing or slotting, full diameter cut, spindle and interface, holder style, etc. The importance is that the tooling database is able to track all these issues. The tooling database will maintain the information of the material being machined along with the machine max rpm, feedrate, horsepower, interface, natural frequency and flexibility. It instantly gives predictable parameters with the ability to log maximum performance of a given cutter assembly once experienced.

With a tooling database, the user is able to input the G-Factor or tool unbalance (in gram-mm) results from their balancing machine along with spindle speed and automatically compute the unbalance forces. By utilizing user-input data on workpiece material, chip-load and depth of cut, anticipated peak cutting forces can be computed. All of the necessary information is then available for the user to make an informed judgement on the required tool balance.

CUTTER GEOMETRY
Cutter geometry plays some role in the ability to machine at any speed. Geometry can give superior chip evacuation by flute gullet or chip breaking. Geometry also allows less force of cut with positive rakes and more force of cut with negative rakes. Chatter is the condition of a cutter jumping out of cut due to its natural occurring frequency or self-excitation. In order for geometry to work optimally, the user should still know a cutter's natural frequency and flexibility readings. This allows the machining operation of that cutter to operate at its maximum MRR. The key is, "To determine better use of the cutter geometry, identify the overall dynamics of the cutter assembly in the machine structure." A tooling database should allow the tracking of comprehensive database information, revealing such parameters taken to complete the highest overall performance of a cutter.

First-Line Estimation of Cutting Performance
Another unique benefit of using a tooling database is the tracking and interpretation of dynamic data. Tool assembly flexibility measurements are becoming more common in today's machine shop. Natural frequencies and flexibility readings are being used more to compare tooling and spindle performance. Additionally, the effect of spindle speed on high-speed machining is becoming more accepted. A tooling database allows for the input of this data, which can then be used - combined with the selected workpiece material - to estimate limit depth-of-cut and optimal spindle speeds.

If dynamic measurement results are not available, fields should be provided to input actual cutting test or machining experience results. The user can then easily track limits, good spindle speeds and maximum depths of cut for each tool. Once this data is obtained for a reasonable tool set, a tooling database will allow reasonable predictions to be made on new tooling given critical parameters such as gage length, arbor-type, tooth count and tool stick-out.