• Shenoy Engg Private Limited

A Special Purpose Machine for Knurling

Many components like handle bars, drive shafts, etc., in bicycle and automobile industries, pump manufacturing industries, etc., need knurling operation on OD, for providing better grip to the mating part. Knurling is normally done in a lathe or in a HMC. But these machines are not designed for taking the plunge load of knurling. Shenoy Engineering Pvt Ltd, one of the reputed SPM (special purpose machine) manufacturers from Bangalore, has developed a dedicated Knurling SPM, which mass-produces knurled components at incredibly high speeds and at low cost of manufacturing.

  On a heavily ribbed, fabricated and stress-relieved machine base, a head stock is mounted. Located in the head stock is the spindle, rigidly supported by 2 pairs of heavy-duty, matched pair angular contact bearings. The spindle, powered by a VFD controlled 3 HP motor, provides stepless spindle speeds from 300 RPM to 600 RPM in a stepless range. Mounted on the head stock spindle is the optionally offered, 3-jaw self-centring conventional or hydraulic chuck.

  On the other end of the base, the tail stock is mounted. The tail stock has 2 different movements – (a) Hydraulically operated to & fro movement of the tail stock spindle for holding the job between centres; and (b) Motorised to & fro movement of the tail stock assembly to take care of varying lengths of the jobs.

  Located between the head stock and the tail stock is the carriage, mounted on which is the specially designed HSS knurling wheel to produce knurled surface on a cylindrical job. Opposite to the knurling wheel, Teflon idle roller assembly counter-supports the job when receiving the plunge load of knurling and prevents the job from bending.

  The carriage moves between the head stock and tail stock with the help of a servo drive, in combination with a HMI (human machine interface), which offers 3 distinct advantages: (1) Selection and ensuring of positioning accuracy with unfailing repeatability is ensured by the servo drive; (2) Servo drive also takes the knurling wheel to the exactly required knurling length, wherever the knurling length required is more than the width of the knurling wheel; and (3) Servo drive makes it possible to produce multiple knurled surfaces of different knurling widths, on different jobs of different dimensions at single or multiple locations. The touch screen enabled HMI facilitates for quick program selection for different jobs, on-machine program edit, insertion of new programs, quick editing of cutting parameters like feed, speed, etc.

  The capacity of the present knurling SPM is designed to accommodate shafts of Ø10 mm min to Ø50 mm max x 500 mm long. Longer shafts can be accommodated either through suitable extension of admit between centres or through a hollow chuck. Cross traverse (traverse for the knurling wheel to plunge) is up to 150 mm through hydraulic cylinder. Ball screw and box nut for longitudinal axis movement, in combination with case hardened male sliding surfaces and Turcite for female sliding surfaces will provide smooth, back-lash free smooth sliding movement, apart from wear resistance.

  A centralised automatic lubrication system provides lubrication to the sliding and rotating parts of the machine at regular intervals. Cutting oil is continuously being pumped to the machining zone from a separate reservoir, fitted with a pump.

  An auto-cycle, operated through the combination of direct, encoder based feedback of servo drive for the longitudinal axis, PLC, feed-end limit switches, sensors, etc., ensures that the knurling operation takes place as programmed with repeat accuracy and with the least human intervention.