STOCK ALLOWANCE - SURFACE FINISH CHART

STOCK ALLOWANCE

When machining a surface prior to Roller Burnishing">


 

STOCK ALLOWANCE - SURFACE FINISH CHART

STOCK ALLOWANCE

When machining a surface prior to Roller Burnishing, stock must be allowed for metal displacement. The amount of stock allowance varies with job conditions, material properties, well thickness of the part, nature of the machined surface and the quality of the surface finish desired.

The accompanying table shows typical stock allowances for furnishing ODís and IDís. However, because of the number of variables involved, these figures should be considered only approximate. An exact allowance can best be determined by roller burnishing an actual work-piece to the desired finish and measuring the amount of stock displaced.

Remember, you should displace only the amount of stock necessary for producing the desired surface finish. Excessive roller burnishing not only accelerate tools wear but also can produce flaking of the burnished surface.

 

 

STOCK ALLOWANCE-SURFACE FINISH CHART

WORKPIECE

INTERNAL SURFACE

EXTERNAL SURFACE

SIZE

RANGE

STOCK

ALLOWANCE

SURFACE FINISH m m Ra (Rt)

STOCK

SURFACE FINISH m m Ra

 

MACHINED

ROLLER

ALLOWANCE

MACHINED

ROLLER

mm

mm

 

BURNISHED

mm

 

BURNISHED

High Ductility Material

 

 

 

 

 

 

 

3.12

0.010

2.0 ( 8 )

0.2 ( 1 )

0.010

2.0 ( 8 )

0.2 ( 1 )

 

0.017

3.1 ( 12 )

0.2 ( 1 )

0.015

2.5 ( 10 )

0.2 ( 1 )

 

 

 

 

   

 

12.25

0.017

1.5 ( 6 )

0.2 ( 1 )

0.012

2.0 ( 8 )

0.2 ( 1 )

 

0.040

3.1 ( 12 )

0.2 ( 1 )

0.025

4.5 ( 18 )

0.2 ( 1 )

 

 

 

 

 

 

 

25.50

0.025

1.5 ( 6 )

0.2 ( 1 )

0.017

2.5 ( 10 )

0.2 ( 1 )

 

0.050

3.1 ( 12 )

0.2 ( 1 )

0.025

4.5 ( 18 )

0.2 ( 1 )

 

 

 

 

 

 

 

50.165

0.040

1.5 ( 6 )

0.2 ( 1 )

0.025

3.1 ( 12 )

0.2 ( 1 )

 

0.075

5.0 ( 20 )

0.2 ( 1 )

0.050

10.1 ( 40 )

0.2 ( 1 )

 

 

 

 

 

 

 

Low Ductility Material

 

 

 

 

 

 

 

3.12

0.010

2.0 ( 8 )

0.4 ( 2 )

0.008

1.5 ( 6 )

0.4 ( 2 )

 

0.017

2.5 ( 10 )

0.4 ( 2 )

0.012

2.3 ( 9 )

0.4 ( 2 )

 

 

 

 

 

 

 

12.25

0.017

2.2 ( 9 )

0.4 ( 2 )

0.012

2.5 ( 10 )

0.4 ( 2 )

 

0.025

3.1 ( 12 )

0.4 ( 2 )

0.018

3.5 ( 14 )

0.4 ( 2 )

 

 

 

 

 

 

 

25.50

0.025

3.1 ( 12 )

0.4 ( 2 )

0.012

2.5 ( 10 )

0.4 ( 2 )

 

0.040

4.5 ( 18 )

0.4 ( 2 )

0.025

4.5 ( 18 )

0.4 ( 2 )

 

 

 

 

 

 

 

50.165

0.040

3.0 ( 12 )

0.4 ( 2 )

0.020

3.1 ( 12 )

0.4 ( 2 )

 

0.050

5.0 ( 20 )

0.6 ( 3 )

0.035

5.0 ( 20 )

0.4 ( 2 )

 

 

 

 

 

 

 

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The chart is guideline only, derived from experiments. Under your own conditions the results may be slightly different. The chart indicate that, in the 25-50 mm range, a hole machined in a high ductile material to 3.1 m Ra and 0.050 mm smaller, than the burnishing tool size, will be burnished to 0.02m Ra. If the hole is finished to 1.5 micro-m Ra before burnishing to 0.025 mm of stock need be left for burnishing to o.2 m Ra.

NOTE : Surface finish can be achieved upto 0.05 m Ra by selecting Pre-burnishing Parameters.

High ductility Materials have more than 18% elongation and less than Rc 32. They include : Annealed Steel, Stainless Steel, Aluminum, Brass, Bronze, Malleable Iron.

Low Ductility Materials have less than 18% elongation & a Max. hardness of Rc. 40. They include : Gray C.I., Modular Iron, Heat Treated Steels, Mg. Alloys, Hard Cu Alloys.

Feeds

The thru style tool is self-feeding ; that is the tool feeds itself into or onto the work. It will feed itself independently of machine feed or any external power. All that is required is rotation. The tool should be allowed to feed at its natural rate without being forced or retarded. On machine equipped with automatic feeds, the machine feed should be slightly more (10-20%) than the natural feed rate of the tool so there will be no possibility of retarding the tool, thereby causing it to release prematurely. In applications on automatic machines where the feed rate of the tool exceeds that of the machine, non-feed cages should be specified.

Full bottoming style tools are supplied with non-feed cages and must be machine feed. With this non-feed design, minimum clearance are required to obtain the closest approach to bottom. Feed rates from 30 to 100% as charted for thru style tools are generally satisfactory for all bottoming applications. The exact feed rate of the tool is therefore governed by the specific machine setup.

If under some circumstances, the feeds and speeds shown below are not suitable for the application, a high helix angle cage may help. This fast feed tool is not recommended except in special cases.

Speeds

The tool is designed for conventional right-hand rotation, and either the tool or the work-piece can be rotated. Rotational speed is not critical, but higher than recommended speeds will reduce tool life. If long-length tools, or tools with extension drive are used, speed should be reduced to prevent excessive whip

SPEED AND FEED RATE CHART

 

 

INTERNAL

EXTERNAL

Burnishing

Speed

** Feed (mm/rev)

* Speed

** Feed (mm/rev)

Diameter

RPM

 

RPM

 

 

 

 

 

 

5

1500

0.12

1000

0.15

12

1000

0.32

700

0.3

40

600

1.3

400

1.0

65

300

1.5

250

1.8

95

250

1.8

200

2.7

165

200

3.4

 

 

 

 

 

 

 

* Speeds may be increased or decreased by 50% to suit special requirement.

** Feed may be increased by 30% to suit special requirement.

Machine Considerations

The tool must be properly aligned with the part in the machine to facilitate the engagement of the tool with the work. A slight misalignment (max. 0.15mm) does not produce any adverse effect on the tool or surface finish produced in the work-piece. However, excessive misalignment in a rigid setup between tool and work-piece will cause bending stress in the tool, resulting in fatigue failure of the mandrel tip. Proper alignment is more important when the tool is rotating because tool whip is more likely than part whip. The tool should be rigidly mounted on the drive shank to prevent any axial movement during the release cycle. This is particularly important for large, heavy tools when operated in a vertical position. A keeper key or binding screw also eliminates any possibility of this tool accidentally coming out of the spindle.

In using the tool on multiple spindle automatics, it is best to mount the tool in a top position to minimize chip contamination from the other cutting operations.

Lubrication

A filter (max. 50mm) in the lube system is recommended to prevent entering of chips and grit into the tool. The tool requires lubrication, but cooling only in case of long work-piece as hydraulic cylinders. Therefore, any light lubricating oil or a rich, soluble oil mixture is recommended. Lubricant should be fed to the tool in a steady of ample volume to provide flushing and cleaning action

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