form cutters or conventional solid-carbide tools. Both meth- ods have several disadvantages: • Form tools oſten create visible cusps on the part surface, especially when the machine tool control is not quick enough to generate a smooth cutting path.
• Te zero rake angle and low helix angle of the HSS cut- ters make it harder to achieve appropriate surface results.
• Use of conventional carbide tools allows only product forms with a radius. In addition, not all radii can be generated due to design limits of the cutter body. When the shortcomings of the tooling made the required
surface roughness unachievable, additional less-reliable opera- tions such as manual polishing or soda blasting were neces- sary. Tose operations were unpredictable in terms of time, costs and quality. To overcome these problems, the Jabro Premier Finisher
design is based on concave and convex sections either tangent or connected with a straight line. Compared to mold and die
Other care and maintenance procedures for these tools are
recommended as well and discussed in more detail below: Handling and logistics: Te tools should be handled with
extreme care as the cutting edge is easily damaged—even fin- gernail contact could result in light wear on the cutting edge. Protection during shipment and transit is indispensable. Tools are covered with a protective wax and sealed inside the pack- aging tubes marked “Handle with Care” and “Do not repack.” Measurements and detection: Within the medical industry,
traceability is a very important requirement to ensure quality in sealed (validated) processes. Terefore all tools are provided with unique laser marking. Reliability and quality standards are set by contactless measurement techniques and sealed grinding procedures. Tool-setting: Te tools can be reconditioned up to five
times; when significant wear is present, safe packaging is nec- essary to prevent uncontrolled wear or damage while in transit during the reconditioning process.
Machining the Co-Cr tibial tray typically can take up to seven separate machining operations.
tools the profile tolerances of the tools are quite generous. However, the manufacturing of these cutters requires special care regarding the cutting edge geometry and the overlap be- tween the concave and convex shapes, areas where the contour starts or ends with a small contour radii, and considerations regarding the tools’ largest diameter. Manufacturing must be controlled to avoid sudden changes
in the pressure of the tool grinding wheel or generation of ex- cessive heat, which may produce areas on the cutting edge that are not sharp enough for the required operation, resulting in a shearing instead of a cutting action. Clean cutting is essential in producing fine finishes in the UHMWPE workpiece. Seco has refined the manufacturing grinding operations
for Premier Finish tool and eliminated any problem areas to produce a constant rake over the whole cutting length with a cutting edge radius of around 5 µm. The Premier Finish tools can be applied between 100
and 200 m/min, dependent on the quality of the CNC control. Generally, with better control systems, higher feed rates are possible. The feed per flute per revolution is normally between 0.004–0.006 times the cutter diameter: for example, between 0.02 and 0.10 mm/flute for a 20-mm diameter cutter.
Cutter Care Normal tool life for a Premier Finish form cutter is be-
tween 1000 and 2000 parts. It is common practice to leave the cutter in the machine until it is worn: taking it out and storing it causes too much risk of damage.
Cleanliness: When the tools are applied on a milling machine
that is also used for cutting metals common for orthopedic implants (titanium/cobalt-chrome alloys and stainless steels) attention should be paid to clean the machine thoroughly. Metal chips will harm the cutting edge of the tool when making direct contact. Terefore it is necessary to have machines equipped with coolant filtering systems sufficient to ensure clean coolant that is free from chips. Te implant supplier should also take into account the quality of the UHMWPE material. Imperfec- tions in the material could result in tool wear due to inclusions. Premature wear of the cutter could be a sign that the machined polyethylene is not clean. In this case, quality in procurement procedures should be point of attention.
Conclusion To productively and profitably fulfill the increasing de-
mand for high-precision orthopedic components and other medical parts, manufacturers of the parts must take advantage of every opportunity to enhance their production technology. A key contributor is tooling technology, such as that provided by Seco for medical component milling operations. Sophis- ticated tools, of course, command a higher price than the basic tools of the past. For example, Premier Finish tools are eight times as expensive as the ballnose cutters formerly used to machine UHMWPE. However, given the features of the cutters and their outstanding capabilities in regard to quality, productivity and consistency, as well as the fact that they can reduce cost per part by up to five times, investment in these cutters is a worthwhile strategy.
Medical Manufacturing 2014 71
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