the stem. Operations for these types of parts are typically rough drilling, rough turning, semifinishing, finish turning and parting off. Choose inserts for these operations that offer process security over long runs. Important factors include insert nose radius, coating, geometry and grade. Selecting a proper nose radius is a key factor in turning
operations. A larger nose radius is advantageous for heavier feed rates, larger depths of cut, stronger edges and increased radial forces. In contrast, the smaller nose radius is better for small cutting depths, less insert strength and also reduces vibrations. Using an insert that is wear resistant, heat resistant
the cutting edge. Such accurate coolant delivery aids in the breaking and evacuation of the chips increasing process sta- bility while helping to lower the temperature in the cutting zone and increase tool life. Radial chip thinning techniques can also help and is an-
other reason for choosing a round insert. Using a round insert for the internal and external acetabular cup will help create thinner chips so evacuating them is no longer a problem. Te radius of the round insert allows the cutting edge to approach the material more slowly increasing engagement. And with longer engagement, chip thickness is reduced.
The same properties that make cobalt chrome an excellent choice as a replacement hip joint also make it problematic to machine.
and increases security will machine more components with fewer inserts. Coatings improve time in the cut by creating a heat barrier towards the cutting zone and chip. From groove milling to surface finishing, select geometries and grades that are designed to work with cobalt chrome. Razor sharp, high edge-line toughness and versatility will provide peak perfor- mance when machining these components.
Cutting Tool Data Knowledge Precise cutting tool data plays a key role in controlling and
lengthening tool life when handling metal alloys this hard and abrasive. Knowing the proper cutting tool data and choos- ing the correct tools are important for process security and productivity and can extend insert and tool life. Productivity is increased when inserts can run a full batch without need- ing to be replaced. Knowing the correct feed rate and cutting speed are important as well. Using a feed rate that is too high causes tool vibrations and pressure that can cause the insert to break and chip. If your cutting speed is too high it creates heat and friction that quickly leads to work hardening. Once work hardening takes place, a domino effect can happen and tool life takes a nosedive as it causes premature wear, inadequate surface finish and insufficient tolerance requirements.
Hips and Chips Chip management is another obstacle when machining
cobalt chrome. Oſten producing long chips that don’t break properly and tend to wind and tangle, cobalt chrome chips can cause unnecessary downtime. Constantly stopping the operation to untangle chips is counterproductive and leads lower output levels and ultimately less profitability. Using high-pressure coolant can help evacuate the chips and at the same time help avoid work hardening by preventing the transfer of heat from the insert back to the material. Using a high-precision coolant will channel coolant directly to
Importance of Surface Finish Surface integrity is an important aspect as to why cobalt
chrome is an appropriate material for hip replacement mate- rial. It’s medically necessary to use a material that can hold up to the wear and tear of the human body for a lifetime. Te surface finish must be excellent not only for a patient’s comfort levels and mobility because it creates less friction, but it must also be primed for any secondary processes that the compo- nents must undergo before they arrive in the operating room. Without a proper surface finish, codes and numbers that are required to be etched into each component for identification and tracking will not be visible. Tis year, medical devices manufactured in the United
States, including hip replacement components, will include a unique device identifier (UDI). Tis unique code will allow patients, health care professionals, manufacturers and federal regulators to track each device. By 2018, every component manufactured in the US must carry this UDI. Shops need to turn out the highest quality components at
the lowest possible cost per part to remain competitive. With an increasing need for prosthetics due to our aging popula- tion, conforming to the uncompromising guidelines and rules of the medical community presents some challenges. While cobalt chrome is one of the hardest, most abrasive materials to machine, those demanding qualities are exactly why it is a desirable material for hip replacement parts. Absorbing weight and allowing mobility, resisting corrosion and providing excellent wear, this material is hypoallergenic, biocompatible and able to be precisely machined for friction- free joint movement. By understanding key factors like tool selection, cutting tool data and chip management, machin- ing a high-quality component may be difficult to achieve, but through proper knowledge, education and technical support shops can overcome these challenges and be successful in this industry.
Medical Manufacturing 2014 41
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216