Carnegie Mellon University, Department of Mechanical Engineering, Pittsburgh, PA 15213, USA.
Med Eng Phys. 2011 Dec;33(10):1234-44. doi: 10.1016/j.medengphy.2011.05.014. Epub 2011 Jul 30.
This paper presents a new thermal model for bone drilling with applications to orthopaedic surgery. The new model combines a unique heat-balance equation for the system of the drill bit and the chip stream, an ordinary heat diffusion equation for the bone, and heat generation at the drill tip, arising from the cutting process and friction. Modeling of the drill bit-chip stream system assumes an axial temperature distribution and a lumped heat capacity effect in the transverse cross-section. The new model is solved numerically using a tailor-made finite-difference scheme for the drill bit-chip stream system, coupled with a classic finite-difference method for the bone. The theoretical investigation addresses the significance of heat transfer between the drill bit and the bone, heat convection from the drill bit to the surroundings, and the effect of the initial temperature of the drill bit on the developing thermal field. Using the new model, a parametric study on the effects of machining conditions and drill-bit geometries on the resulting temperature field in the bone and the drill bit is presented. Results of this study indicate that: (1) the maximum temperature in the bone decreases with increased chip flow; (2) the transient temperature distribution is strongly influenced by the initial temperature; (3) the continued cooling (irrigation) of the drill bit reduces the maximum temperature even when the tip is distant from the cooled portion of the drill bit; and (4) the maximum temperature increases with increasing spindle speed, increasing feed rate, decreasing drill-bit diameter, increasing point angle, and decreasing helix angle. The model is expected to be useful in determination of optimum drilling conditions and drill-bit geometries.
本文提出了一种新的骨钻热模型，该模型可应用于矫形外科手术。新模型结合了钻头和切屑流系统的独特热平衡方程、骨骼的普通热扩散方程以及钻头尖端因切削过程和摩擦产生的热量。钻头-切屑流系统的建模假设轴向温度分布和横截面的集中热容效应。新模型使用针对钻头-切屑流系统定制的有限差分方案进行数值求解，并与骨骼的经典有限差分方法相结合。理论研究涉及钻头和骨骼之间的热传递、钻头向周围环境的热对流以及钻头初始温度对发展热场的影响。使用新模型，对加工条件和钻头几何形状对骨骼和钻头中产生的温度场的影响进行了参数研究。该研究的结果表明：（1）随着切屑流量的增加，骨骼中的最高温度降低；（2）瞬态温度分布受初始温度的强烈影响；（3）即使钻头尖端远离钻头的冷却部分，钻头的持续冷却（冲洗）也会降低最高温度；（4）最大温度随主轴速度、进给速度、钻头直径、顶角和螺旋角的增加而增加。该模型有望用于确定最佳钻孔条件和钻头几何形状。
