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Manufacturing Processes > Machining processes > Planing and Shaping

 

Planing and Shaping

 

Process description

The removal of material by chip processes using single-point cutting tools that move in a straight line parallel to the workpiece surface with either the workpiece reciprocating, as in planing, or the tool reciprocating, as in shaping. Simplest of all machining processes.

Materials

All metals (mostly free machining).

Planing and Shaping

Process variations

  • Double housing planer: closed gantry carrying several tool heads.
  • Open side planer: open gantry to accommodate large workpieces carrying usually one tool-head.
  • Horizontal shaping: includes push-cut and pull-cut.
  • Vertical shaping: includes slotters and key-seaters.
  • Wide range of cutting tool geometries and tool materials available.

Economic considerations

  • Production rates ranging 1–50/h.
  • Lead times vary from short to moderate.
  • Material utilization is poor. Large quantities of chips are generated, which can be recycled.
  • Flexibility is high. Little dedicated tooling and setup times are generally short.
  • On larger parts, the elapsed time between cutting strokes can be long making the process inefficient. Can be improved by having the cutting stroke in both directions, using several cutting tools and/or machining several parts at once.
  • Other processes, for example, milling or broaching, may be more economical for larger production runs of smaller parts.
  • Planing machines are usually integrated with milling machines to make them more flexible.
  • Least economical quantity is one. Production volumes are usually very low.
  • Tooling costs are low.
  • Equipment costs are moderate to high, depending on machine size and requirements.
  • Direct labor costs are high to moderate. Skilled labor may be required.
  • Finishing costs are moderate. Normally requires some other machining operations for finishing.

Typical applications

  • Machine tool beds
  • Large castings
  • Die blocks
  • Key-seats, slots and notches
  • Large gear teeth

Design aspects

  • Complexity limited by nature of process, i.e. straight profiles, slots and flat surfaces along length of workpiece.
  • As many surfaces as possible should lie in the same plane for machining.
  • Rigidity of workpiece design important in preventing vibration.
  • Minimum section less than 2 mm, but see below.
  • Minimum size limited by ability to clamp workpiece to machine bed.
  • Maximum size approximately 25m long in planing; 2m long in shaping.

Quality issues

  • Machinability of the material to be processed is an important issue with regards to: surface roughness, surface integrity, tool life, cutting forces and power requirements. Machinability is expressed in terms of a ‘machinability index’ for the material.
  • Adequate clearance should be provided for to prevent rubbing and chipping of the cutting tool on return strokes.
  • Cutting tools require chip breakers for ductile materials, because the strokes can be long during machining and the swarf may tangle and pose a safety hazard.
  • Selection of appropriate cutting tool, coolant/lubricant, depth of cut, feed rate and cutting speed with respect to material to be machined is important.
  • Coolant also helps flush swarf from cutting area.
  • It can produce large, accurate, distortion free surfaces due to low cutting forces and low local heat generation.
  • Surface detail is fair.
  • Surface roughness values ranging 0.4–25 µm Ra are obtainable.
  • A process capability chart showing the achievable dimensional tolerances is provided. Note, the tolerances on this chart are greatly influenced by the machinability index for the material used.

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