In-situ tool wear monitoring and its effects on the performance of porcine cortical bone drilling: a comparative in-vitro investigation
© The Author(s). 2017
Received: 4 November 2016
Accepted: 17 January 2017
Published: 25 January 2017
Drilling is one of the most widely used process in orthopaedic surgical operation and the same drill bit is used a number of times in hospitals. Using the same drill bit a several times may be the cause of osteosynthesis and osteonecrosis.
In the present work, the effect of repeated orthopaedic surgical twist drill bit on the tool wear, force, torque, temperature and chip morphology during porcine cortical bone drilling is studied. Results were compared with rotary ultrasonic drilling (RUD) on the same bone using a hollow drill tool coated with diamond grains. A sequence of 200 experiments (100 with each process, RUD and CD) were performed with constant process parameters.
Wear area on the drill bit is significantly increased as the drill bit is used repeatedly in CD, whereas no attritious wear was found on the diamond coated grains in RUD.
Comparative results showed that cutting force, torque and temperature increased as a function of tool wear in CD as the same drill bit was used a number of times. No significant variation in the cutting force and torque was observed in RUD as the number of drilled holes increased.
In orthopedic or trauma surgical operations drill bit is used number of times to make holes in bones. Using the same twist drill bit a number of times leads to decrease in its cutting efficiency during the bone drilling process. A significant tool wear is formed on the cutting edges of the drill bit due to reuse, which may lead to increase in the frictional forces and heat between the bone and the drill bit. In this direction, few studies have been reported in the medical field, which are summarized below:
(Allan et al. 2005) performed in vitro study on a pig mandible to investigate the effects of drill wear on the change in bone cutting temperature using 3 different drill bits (n = 0, n =600 holes drilled, n = used many times in operation theater). They reported that with increase in the drill wear, temperature increased significantly. It was also observed that the drill bit obtained from the operation theater generated a maximum rise in temperature as compared to the other two types of drill bits.
(Oliveira et al. 2012) conducted drilling experiments on bovine bone with twisted stainless steel and ceramic drills to find out the relation between the thermal changes and drill wear. They found that temperature increased with the drilling depth and thickness of cortical bone. Their investigations suggested that depth was the predominant factor influencing the temperature variation in bone drilling. Further, it was concluded that stainless steel drill bit had more tip wear as compared to the ceramic drill bit.
(Chacon et al. 2006) investigated the effect of repeated drill bit (25 times) on temperature using a femura cortical bone and found that temperature significantly increased with the use of repeated drill bit. They reported that drill tool was worn after being used a number of times.
(Queiroz et al. 2008) performed the study on a rabbit’s tibiae to investigate the effect of repeated drill bit (40 times) on the bone cell viability. They concluded that cell viability decreased in the bone matrix using a repeated drill bit. SEM was used to analyze the wear on the drill bit and they observed that it increased consistently. In another in-vitro study on rabbits, (de Souza et al. 2011) concluded that significant heat was generated if the same drill bit was reused after 50 times and a worn drill bit could damage the bone tissue during drilling.
(Jochum and Reichart 2000) investigated the influence of titanium repeated drill bit, of diameter 3.2 mm (51 times) on the temperature using pig mandibles. In their in vitro study, rotational speed was 1200 without any irrigation. They reported a significant amount of increase in temperature if the same drill bit was used more than 40 times. They also found that the sharpness of the drill bit edge weakened, if used number of times.
Recently (Staroveski et al. 2015) performed an experimental investigation on cortical bone to study the effect of tool wear on force and torque. They reported that temperature continuously increased using a repeated uses of drill bit.
In the last three decades, various studies have been reported on the monitoring of drill wear which is focused on industrial applications (Jantunen 2002). However, drilling method in surgical operation theater is different as compared to industrial application. In trauma or orthopaedic surgical drilling, temperature should be lower than 47 °C to avoid thermal necrosis (Lundskog 1971; Eriksson et al. 1984; Krause 1987; Augustin et al. 2008). Cutting forces (Alam et al. 2009; Alam et al. 2011; Wang et al. 2014a) and torque (Alam et al. 2011; Wang et al. 2014a) should also be minimum. Using a drill bit repeatedly increased the temperature (Jochum and Reichart 2000; Allan et al. 2005; Chacon et al. 2006; Queiroz et al. 2008; de Souza et al. 2011; Oliveira et al. 2012) and force (Staroveski et al. 2015) significantly which may cause to decrease the strength of internal fixation (Allan et al. 2005).
Measurement of drill tool wear during bone drilling is not possible, but it can be measured by the wear area on the tool after the drilling. In the present study, tool wear on drill bit during the CD of porcine cortical bone has been measured using the white light microscope and its effect on the cutting force, torque and temperature has also been studied. Results were compared with the RUD using a hollow drill tool coated with diamond grain particles. The aim of the present study is to introduce the RUD on bone and to investigate the effect of tool wear on the cutting performance.
Bone specimen details
In-vitro comparative study has been performed on the male diaphyseal part of porcine cortical bone (thickness of 4–5 mm) which was obtained immediately after slaughtering. Four porcine cortical bones were purchased from the local slaughterhouse and preserved immediately in a buffered solution of 10% formalin and 90% saline water. The porcine was around one year old and 88 kg in weight. The proximal and distal ends of the cortical bone have been removed by using a plane hacksaw.
In vitro experimentations
Specification of hollow drill tool and twist drill bit
Diamond coated hollow drill tool
Twist drill bit
Number of cutting lips
Areal average abrasive/grain density
Tool base material:
Tool shank material
Abrasive/grain coated method
A stand with adjustment features was designed and fabricated for holding the microscope (in situ tool wear measurement). Horizontal and vertical axis (X-Y-axis) was adjustable with sliding movements and Z- axis was the base of the stand which was also movable. A rotational feature was provided for rotational movement (0° to 360°) of the microscope with horizontal arm (X-axis) as shown in Fig. 1.
A sequence of 200 experiments were performed at room temperature, (100 with each drilling process) without any irrigation, using constant process parameters i.e., spindle speed of 1500 rpm, feed rate of 10 mm/min, and drill diameter of 4.5 mm. Vibrational frequency of 20 kHz and amplitude of 16 μm was used for the RUD. These parameters were selected on the basis of the in vitro bone drilling study performed by (Gupta and Pandey 2016a; Gupta and Pandey 2016b). Drilled holes were made to a depth of 4 mm with both the processes.
Dino Lite microscope (Dino-Lite Pro II AM411T) was used to capture the images of the wear on the drill tools used in this work. Images were captured at n = 0, i.e. new drill tool and thereafter for every 5th experiment (5th, 10th, 15th….100th). These images have been further analyzed in the microscopic image analyzer software (Digimizer) for measurement of the wear on the respective tools. The Chip morphology was also studied after the 1st, 5th, 10th, 15th …. 100th experiments. For measurement of wear on the drill bit, 21 images were captured for CD and 63 for hollow drill tool, and for chip morphology a total of 42 images were captured for both the drill tools.
In total 126 values were measured (63 with each process) for cutting force (42), torque (42) and temperature (42). 6 axis Schunk dynamometer (Delta IP68) was used to measure the cutting forces and torque, which was mounted on the table of the machine (Fig. 1). Temperature was measured by digital thermometer with thermocouple (K-type, Cu-Al) probe. The probe of the thermocouple was inserted (in a predrilled hole of diameter 0.6 mm) to a depth of 4 mm at a distance of 0.5 mm from the drill test hole. Cutting force, torque and temperature were measured simultaneously at the 1st, 5th, 10th, 15th …. 100th experiments for CD and RUD. All the mentioned measurement equipment’s were calibrated and checked before performing the actual experiments.
Tool wear mechanism
Cutting force and torque
On the other hand, no significant effect on cutting force and torque was observed while using a reused hollow drill tool in RUD on cortical bone [Fig. 6]. Whereas, (Cadorin and Zitoune 2015) reported that cutting force increased to 16% after the 100th drilled hole w.r.t. 1st drilled hole while drilling on a carbon fiber reinforced polymer with hollow drill tool coated with diamond particle (without any ultrasonic vibration).
Temperature and chip morphology
ANOVA of force, torque and temperature for RUD and CD
p > 0.05
P < 0.05
p > 0.05
P < 0.05
P < 0.05
P < 0.05
Statistically significant difference was found from the ANOVA analysis (Table 2) between the two drilling processes on the force and torque for repeated drilling. Insignificant effect on the force and torque was found for repeated hole drilling by RUD, as their p values are greater than 0.05, and adjusted R2 for force and torque is also–0.019 and –0.030 respectively. In other words, a statistically significant effect on force and torque was found for CD. P value of force and torque was found to be less than 0.05 and corresponding adjusted R2 is 0.898 and 0.965 respectively.
A positive correlation was found between the two drilling methods on the increase in temperature for the repeated drilled holes. RUD and CD produced a statistically significant effect on the rise in temperature (P < 0.05), and their adjusted R2 is 0.985 and 0.963 respectively.
The change in the cutting force, torque (Alam et al. 2011) and temperature (Alam and Silberschmidt 2014) is affected by the drilling parameters including the feed rate, applied force, spindle speed, drill geometry, cooling system etc. In this work, effect of repeated drilling by two drilling methods i.e. CD and RUD were compared for the cutting force, torque, temperature, tool wear and chip morphology. RUD is a non-traditional machining process in which ultrasonic vibrations are given to the hollow drill tool. Cutting mechanism in this process is different as CD (Gupta et al. 2016; Gupta and Pandey 2016a; Gupta and Pandey 2016b). In RUD the tool work contact ratio is minimal due to the ultrasonic vibrations, whereas in CD, there is direct contact between the tool and the workpiece. As a result, more frictional forces are generated in CD as compared to RUD. Bone is different than metal or composite as it is a complex material (Yu et al. 2005) in the form of layers containing a soft tissue, hard tissue, bone marrow and protein fibers. The phenomena of wear on the tool is characterized by friction between the drill bit and workpiece (Park et al. 2011; Çelik et al. 2015).
As the number of drilled holes increase, the cutting edge of a drill bit becomes dull and its sharpness diminishes which may be the cause of increase in the friction between the drill tool and bone in CD. The material is eroded from the tool in micro and sub - micro level [Fig. 3(b-d)]. Therefore, cutting forces, torque and temperature increase significantly as the number of drilled holes increase.
In RUD, material is removed by the cutting action of the diamond grain and hammering action of ultrasonic vibrations, so intermediate contact is generated between the workpiece and the bone. As a result, less amount of friction is generated. Therefore, no wear on the abrasive particles was observed on the hollow drill tool and no dislodgment of the diamond grains was also observed after the 100th experiment.
However, (Zeng et al. 2005) reported that after the 16th experiment diamond grains were dislodged, while drilling a SiC with rotary ultrasonic machining. They also concluded that the color of thee diamond grains changed, due to increase in the temperature. But no change in the color of diamond grains was observed, in the RUD of bone, which also shows that temperature of these diamond grains was low during RUD. This may be due to low friction and temperature generated at the interface of the bone and diamond grains.
The worn area on the orthopaedic twist drill bit increased as it was used a number of times in CD, while in RUD, no attritious wear was found on the diamond grains
In CD, cutting force, torque and maximum change in temperature increased continuously as the number of drilled holes increased. However, in RUD only cutting temperature increased gradually with repeated drill tool.
After performing the 100th experiment in RUD, no significant variation in the cutting force and torque was observed.
Chip morphology changed as the drill bit was used repeatedly in CD, while no change in chip morphology was observed in RUD.
RUD generated lower cutting force, torque and temperature with respect to CD, which can eliminate the burring of soft tissue in orthopaedic bone drilling process.
Statistical results also showed that reused drill bit had a significant effect on the cutting force, torque and temperature in CD.
Authors are grateful to Professor, Ravi Kumar Gupta, Department of Orthopaedics, Government Medical College Hospital Chandigarh for providing the orthopaedic drill bit and his valuable suggestions to carry out this work. Gratitude is also given to Dr. Asit Ranjan Mridha, Assistant Professor, Department of Pathology, All India Institute of Medical Sciences (AIIMS) New Delhi for helping in the preservation of bone specimen.
The present study was financially supported by EPSRC-UK and DST-Delhi (India) sponsored project “MAST”.
Both the authors contributed to preparation of the paper. Both authors read and approved the final manuscript.
The authors declare that they have no competing interest.
Ethics approval and consent to participate
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