Product category:
Tool and cutter grinding
News Release from: Anca Pty | Subject: CNC tool and cutter grinding
Edited by the Manufacturingtalk Editorial
Team on 29 May 2002
Is CNC tooland cutter grinding for you?
- read on
The purpose of this paper is to attempt to give a better understanding of CNC tool grinding, the advantages of CNC ground tools, case histories of actual usage its benefits and its justification.
We at ANCA (UK) are constantly being queried by customers on the benefits of CNC ground tools Vs the conventional manually ground tools The purpose of this paper is to attempt -in laymen terms -to give a better understanding of CNC tool grinding, the advantages of CNC ground tools, case histories of actual usage and additional benefits in the justification of a CNC Tool Grinder
This article was originally published on Manufacturingtalk on 25 May 2004 at 8.00am (UK)
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For simplicity, we will use the grinding of a simple 4 flute high speed endmill for our example.
In all manual grinding applications using Aluminium oxide grinding wheels and grinding with no coolant, a significant amount of heat is generated which in turn is transferred to the primary cutting edge of the tool.
In manual grinding, the tool is held either in a collet or ground between centres but in either case, when grinding the primary and secondary angles on the OD, the tool must be supported on this "finger", the grinding wheel must be turning in the direction downward to keep the tool on the "finger".
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Heat generated from the dry grinding process is therefore forced into the primary angle.
The heat generated actually breaks down the hardness of the cutting edge and although the tool may appear to be sharp, further regrinds only cause further weakening of the hardness of the tool.
Manual grinding is very dependant on the skill of the actual machine operator, something we see as a dying art as there are virtually no Apprenticeships available at the present time for Tool and Cutter Grinding.
The skill of the operator and his ability to create the same geometry consistently on a daily basis contributes directly to the cutting ability of the tools he is grinding.
His knowledge of the correct geometry needed to be produced on the different tools to obtain the desired speeds and feeds for today's sophisticated CNC Machine tools; and exotic metals being machined must be very demanding and his ability to re-create these angles on a consistent basis results in a highly skilled individual.
The number of set-ups, operations and machinery required is of great importance in the manual application.
The simple regrind of a endmill will require at least 3 set-ups - one for OD, one for end face, one for gashing and a fourth if corner radius or ball nose is required.
If step tools or drills are involved, then additional machinery and set-ups are required.
Floor space to handle all of these machines must be considered when reviewing the manual application.
Manufacturing tools from solid blanks is a very slow and time-consuming operation in a manual shop.
The heat limitations of grinding wheels used and lack of necessary coolant, limits the amount of stock that can be removed in a single pass.
To summarise, manual tool grinding is very operator dependant upon the use of a variety of different machines and set-ups to achieve the consistency in tool geometry found in today's modern CNC machine shops.
The use of a CNC tool grinder significantly increases both the tool regrind life and the finished parts per tool produced.
Tools ground on a CNC grinder are ground under a high pressure flood coolant environment using the latest super-abrasive technology.
CBN or Diamond wheels have been perfected in the last few years to stand up to the rigours of CNC tool grinding and have proven to outlast the conventional abrasive by a 50 to 1 ratio and in some cases much higher than this figure.
CNC has eliminated the need for a "finger" for the tool to rest on and allows for the wheel to be run in reverse, which produces a finer cutting edge.
By being able to control the wheel speed and the feedrate of the grinding pass combined with the high pressure/volume of coolant, the operator is able to obtain desired surface finish on the tools being ground.
The high pressure coolant eliminates any heat build up that occurs as well as acting as a lubricant for the grinding wheel and assists in the cleaning of the grinding wheel to assure that the wheel cuts properly.
The use of one CNC machine will eliminate at least 3 machines in every case.
Let's examine the regrind of a simple 4 flute endmill.
In the manual shop you need at least 3 machines to sharpen the tool and additional equipment or set-ups for corner radius or ball nose.
On a CNC grinder all of these steps are obtainable on one machine.
Plus in most cases the operator can be grinding something else while the CNC machine produces his finished tool, or selecting the required file from the control for the next tool to be ground.
End mill design and manufacturing processes have changed dramatically in the last ten years.
The materials and combination of steels found in today's cutting tools changed to meet the demands of the user.
The exotic metals such as stainless, Inconel and Titanium have forced the manufacturers to develop tools to cut these materials.
CNC allows the operator to create geometry to handle these very abrasive, hard to cut materials.
CNC has allowed for the creation of the geometry and the ability to recreate them when desired.
Tool geometries previously almost impossible to create can be easily manufactured and reground for exotic composite and laminate materials.
Today's high speed machining centres with speeds up to 30,000 rev/min have also added to the requirement of the tool manufacturer to produce geometry to allow for these speeds.
The regrind application for CNC has also increased accordingly.
The ability to produce one off tools on an "as need" basis has also added to the importance of CNC tool grinding.
It is much more economical to keep hardened drill blanks in stock and write a program for your CNC Grinder to produce your tool in under 1 hour or less, rather than to wait upwards of 3 months for a special tool from an outside vendor.
The CNC tool grinder has eliminated conventional methods of producing cutting tools.
In the past the manufacturer was forced to mill softened blanks, heat treat to a desired hardness, stress relieve and finish grind.
With CNC finished hardened blanks are ground, eliminating steps in the manufacturing process.
Inconsistency found in the tooth spacing of conventional ground tools has virtually been eliminated by the CNC tool grinder.
The position of each flute in relationship to the centre line of the cutting tool determines the even distribution of cutting forces on the tool to assure equal chip load and chip removal.
Uneven spacing of the teeth results in one or more teeth taking the greater cutting load which results in poor finishes, less parts finished per tool and premature tool failure.
In summary, the CNC tool grinder gives consistency tool to tool, the ability to create and hold geometry, eliminates machinery, set-ups and operations, saves floor space, and eliminates the need for a high inventory of finished cutting tools when the ability to create tools from blanks exist.
With CNC, when you make a change, you can see the change.
In this section we will point out additional features that will assist in the justification of a CNC tool grinder.
Each point will be different for each application because the total volume and styles of cutting tools ground varies for each application but in general it will provide other areas to look at when justifying a machine.
The benefit of being able to run the milling machine at the manufacturers intended surface feet per minute is a measurable advantage but one that is rarely considered when purchasing a CNC tool grinder.
A CNC ground tool equally distributes cutting forces on each flute and with the correct geometry for the material being milled on the cutting tool, the benefits over conventionally ground tools is enormous.
The cost of maintenance on spindle bearings, motors, etc of the machining centre is something always overlooked.
An improperly ground tool throws the spindle out of balance causing unnecessary wear.
Heat is a major factor in the maintenance of CNC machining centres.
Improperly ground tools cause excess wear on bearings, creating heat that breaks down both lubricants of the machine but also in the coolant used on the machining centre.
Costs for electricity rise because of the improperly ground tools.
This is a statement that might sound ludicrous but stop to think, a job that takes 10 minutes with improperly ground tools could be finished in 8 minutes.
Again this goes back to being able to run the Machining Centre at optimum feeds and speeds.
Having the ability to grind the tool in the same tool holder used on the Machining Centre is a definite plus at obtaining the optimum concentricity.
Most CNC tool grinders come with a universally accepted ISO taper, which allows for the same holding as found on Machining Centres.
The addition of Probing inside the CNC grinder as a standard cycle feature has virtually eliminated the need for off line set-up stations and people to man these areas.
Probing is advancing daily and there are tracking systems available capable of tracking the new Cutting Tool through its entire "life-cycle" in production.
This is a feature that assists greatly in the inventory problem faced by most large users of cutting tools.
CNC ground tools give the user the advantage of being able to predict when to change tools, when to regrind, when to set-up for the next job or part run and assists greatly in predicting profitability.
In process SPC analysis, using the probe can optimise the grinding conditions, predict trends such as wheel wear and produce measurement graphs to accompany tools.
How do you do a justification for each individual application? We again are constantly asked this question.
Basically, every application is different but you will have to look at the following: current cost for new tools, cost for refurbishing these tools, manpower to regrind, age of people in grinding areas, time studies on parts per tool off the Machining Centres, turnaround time for special tools, floor space for grinding area, do you wish to manufacture your own tools and save monies, age of present equipment, future business and tools required to obtain this business, competition and why they can underbid on project maintenance costs and present inventory levels of tools in stock.
ANCA encourages you to look at other uses for the RGX CNC Tool Grinder.
Basically we have 8 axes of simultaneous interpolation with full Creep Grinding ability.
If the part will physically fit into the machine work envelope both from a size and weight standpoint, then it is just a matter of fixturing and developing software to grind.
We have extensive knowledge working with the grinding wheel manufacturers, to develop grinding wheels to grind intricate parts.
Imagine the savings to your customers.
In typical manufacturing processes, parts in a softened state are machined then heat treated and then finish ground.
The scrap rate resulting from distortion caused in heat treating varies from application but usually averages from 5 to 20 percent.
By the use of a hardened part and RGX your customer has the ability to produce parts from the hardened blank thus eliminating 2 or 3 steps in the traditional manufacturing process and the scrap rate is virtually eliminated.
If the parts have slots, forms, shapes, flats, helical configuration or any combination, they should be considered for the RGX.
One of our users who manufacturers solid carbide endmills, reports that by utilising the RGX he has been able to eliminate 4 steps in the manufacturing process of his tools.
The manual operations included machines for fluting, grinding of primary and secondary, end geometry, gashing and corner radius.
By switching to CNC he now flutes on a dedicated fluting machine and finish grinds all of the other operations on the RGX.
Machines and operators have been eliminated plus his consistency from tool to tool has risen over 80% versus the manual steps he previously utilised in the production cycle.
These are just a few examples of actual savings in the grinding process of various tools.
A significant justification is the actual parts per tool that came off the CNC machining centre by utilising the CNC ground tool.
We have been told by the above Automotive customer, that his average increase in production has risen 38% but in one particular job - the staggered tooth side-milling cutter production increased almost 220% by simply switching to the CNC ground mill.
He also noted that his inventory of mills has been reduced by 70% and that he is doing a study at present to determine the set-up cost reduction.
We trust that this information will be of value to you in your consideration of purchasing an ANCA Fastgrind CNC Tool Grinder.
Case histories - Automotive Application 1in x 4 flute carbide endmill manual grind took 3 set-ups and grinding time of 18 minutes.
Same tool on CNC Grinder - 1 set-up and a grinding time of 4 minutes.
2in x 3 flute core drill manual grind to 4 set-ups with grinding time of 32 minutes.
Same tool on CNC Grinder - 1 set-up and 4 minutes and 47 seconds grinding time.
3.
1.5in x 6 flute spotface tool manual grind took 4 set-ups and grinding time of 34 minutes.
Same tool on CNC Grinder - 1 set-up and 5 minutes grind time.
4.
14"inx 20 staggered tooth side milling cutter took 10 set-ups and 2 hours and 14 minutes grinding time.
Same tool on CNC Grinder - 2 set-ups and 18 minutes grinding time.
5.
1.5in x 6 flute chamfering tool manual grind took 1 set-up and grinding time of 12 minutes.
Same tool on CNC Grinder - 1 set-up and 2 minutes 49 seconds grind time.
1in x 6 flutes 3 steps - steptool manual grind took 6 set-ups and 36 minutes grind time plus each step had to be checked on Shadow Graph after each grind.
Same tool on CNC Grinder - 1 set-up and grind time of 3 minutes and 40 seconds.
1in x 4 flute gun reamer manual grind took 3 set-ups and grind time of 18 minutes.
Same tool on CNC Grinder - 1 set-up and 4 minutes and 38 seconds grind time.
8.
10in x 14 flute milling cutter manual grind took 2 set-ups and grinding time of 22 minutes.
Same tool on CNC Grinder - 1 set-up and grinding time of 6 minutes 15 seconds.
9.
2in x 4 flute ball nose tool manual grind took 4 set-ups and grinding time of 18 minutes 30 seconds.
Same tool on CNC Grinder - 1 set-up and grinding time of 3 minutes 57 seconds.
1.5in x 4 flute x 2 step, step drill manual grind took 4 set-ups to grind step lengths plus each step had to be checked on shadow graph and a grind time of 14 minutes 40 seconds plus another set-up was needed to grind point resulting in a total grind time of 16 minutes.
Same tool on CNC Grinder - 1 set-up with a grind time of 4 minutes 12 seconds.
These are actual case histories of times given to ANCA by one of our users in the automotive industry.
ANCA Inc Michigan, USA Telephone (810) 477 5588 Facsimile (810) 477 2218 ANCA (Europe) Ltd Mannheim, Germany Telephone (0621) 338 100 Facsimile (0621) 335 278 ANCA Pty Ltd Melbourne, Australia Telephone (613) 9720 3077 Facsimile (613) 9720 4412 ANCA SARL Sassenage, France Telephone (04) 76 53 50 00 Facsimile (04) 76 26 46 14.
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