Twist Drill and Method of Drilling Composite Materials

        Twist drill and method of drilling composite materials

Publication Number: US20140169898 A1

Publication Date: 19 June 2014

Patent Holder: Wan Tsin Goh

Field of the invention:

The morphology of a twist drill used for drilling composite consists of – a) Shank b) Cutting edge c)    Chisel edge d) Secondary chisel edge e) Drill tip. The drilling cutting parameters of such a drill are drill tip angle from 145 to 165 degree, point angle 70 to 100 degree. The flute of the drill bit has a helix angle of 45 to 55 degree. Stack drilling method is used when composite consists of laminate material, carbon fibre reinforced plastic, and glass fibre reinforced plastic. It focuses on thrust force, other cutting forces, delamination etc. against drilling parameters feed, speed, depth of cut & type of tool materials while drilling in composite materials.

Background:

The present development identifies with twist drill bits and specifically twist drills adjusted for penetrating, particularly computerized drilling of composite materials like fibre reinforced plastic (FRP’s).

CFRP are mostly used for making the structure of aircraft. The challenge behind such materials is the quality of the holed surface which is obtained. For such materials drilling is very difficult and quality obtained with conventional drill is poor. To improve upon this limitation a twist drill bit of different helix is used but its manufacturing is quite difficult.

The average life of a twist drill is around 60 holes which implies a large no. of it are required in manufacture of an aircraft. So, the tool life needs to be improved.

Kennametal provided this feature which not only can make holes of good quality but also have much better tool life. The proposed idea uses a tungsten carbide drill bit which uses a diamond as coating and its angles are quite reliable.

Excessive heat generation during drilling of composite materials results in delamination as more heat causes the matrix to melt. Power consumption and delamination can be reduced by lowering the thrust force.

In the latest innovations of drill bits the lamination can be more than 5 or 6 layers. Stack drilling is the term for drilling such composites. The fibres can be either continuous or chopped.

Important Claims:

1. A twist drill bit comprises of a shank, tip, chisel edge, body, flute, and secondary chisel edge, point angle at tip & helix angle of flute. Present innovations found that for better tool life constant high helix angle, small point angle & large secondary chisel edge angle are required. Suitable helix angle should be around 45 – 50 degrees. Chisel angle should be around 110 – 125 degrees. Primary relief angle is 15° to 25°. Secondary relief angle is 20° to 25°. Axial rake angle should be 5 – 8 degree. The diameter of twist drill bit should be around 2 to 15 mm. Twist drill bit should be up of cobalt matrix of tungsten carbide.

1. A regrinding technique which includes the progression of regrinding a drill to frame a twist drill bit having a shank & a drill body.

1. Type of drill bits used is the most prominent factor for influencing the of thrust force which is then followed by spindle speed and also with increase in feed rate the thrust force increases. The thrust force obtained are less for diamond coated carbide drill and multi layered Tin coated cemented carbide drill.

1. For delamination it was shown that all machining parameters including feed, speed & depth of cut failed the test and their effect is very less. The delamination at the entry and exit of a twist drill are affected by different parameters which means that at entry of twist drill it is the feed rate which is the most significant factor affecting delamination whereas at the exit of the twist drill it is cutting speed.

1. From the various types of drilling in CFRP it is step core drill which offers maximum thrust force in comparison with others. The diameter ratio and feed rate of step core drill affects the thrust force. The thrust force varies inversely with the diameter ratio. For drilling of CFRP materials high diameter ratio, lower feed rate and high speed are the optimum criteria.

1. A method for production of a twist drill which is used for composite materials drilling can be manufactured by following a set of procedures which includes:

I: To establish a flute from front to rear end which is helical in shape and having helix angle 45 to 55 degrees

ii: At the end of the flute a cutting edge is to be formed

iii: Point angle of 70 to 100 degree is to be carved out

iv: Maintaining the value of chisel angle (secondary) in between 140 to 165 degrees.