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Cannulated or Solid Raw Material? Considerations for Reducing Launch Time, Increasing Manufacturing Efficiency

The speed to launch new products in the orthopedic industry has been and continues to be critically important. With the increasing time required in early product development and regulatory stages, shortening manufacturing time is one of the few areas of opportunity remaining for reducing the time to launch new products. Additionally, device companies are continually pressuring contract manufacturers to reduce costs. Use of cannulated raw material can reduce manufacturing time and improve manufacturing efficiency.

The minimally invasive surgery market, according to Acumen Research and Consulting, is expected to grow at a CAGR of around +9.6% from 2019 to 2026 and reach the market value of about $33.8 billion by 2026. Minimally invasive surgery often drives the need for both cannulated surgical instruments and implants, assuring the need for such devices in the future.
Various options are available for manufacturing cannulated instruments or implants. Traditional gun drilling machines have been used for years to drill deep holes. Using cannulated raw material has also been an option that allows many parts to be completed in one machining operation. Drilling within CNC machines has become common, using both gun drills as well as specialty deep-hole twist drills. However, great opportunities for improvement exist when parts are currently, or are planned to be, drilled in Swiss type CNC machines.

To accurately evaluate use of cannulated raw material vs. using solid bar, one must carefully consider the complete impact of the two options. Traditionally, the comparison of the two options was simply:

Cost of buying cannulated material vs. cost to make the hole in the CNC

This simplistic approach rarely captures the full impact of using cannulated material. Let’s first look at an example of an instrument made from stainless steel.

Instrument Example

driver

Exhibit 1: Cannulated driver, 17-4 stainless steel, 4” length, 0.171” OD, 0.049” ID, AO Quick Connection, T8 Torx


For the example in Exhibit 1, the cost of 17-4 precipitation hardening stainless steel in .187” diameter solid bar is $1.07 per foot while cannulated material is $32.83 per foot. The cost of the raw material is simply the length of the part times the cost of the material. Allowance for kerf and bar drop needs to be considered in determining length. Using a part length of 4.0”, a kerf of 0.08” and a bar drop of .21” per piece, the cost of solid bar is $0.38 and cannulated bar is $11.75. The cost of the raw material can easily be calculated using the following formula:

cannulated material formula 1

To calculate the cost of drilling the cannulated hole in the Swiss, we must consider both the cost of the time to drill the hole and the cost of the drill bits. The following formula is used to calculate the cost of drilling the hole. A fully burdened shop rate of $70 per hour, which includes labor and all fixed and variable overhead, will be used in this example along with the drilling feed rate of 0.67” per minute.

cannulated formula 2

Using this formula, the hole drilling cost is $6.97.

Gun drill bits used to make deep holes can be expensive, ranging from $90 to $140 for small diameters. For this example, we will use $100. Caution must be taken when using these long small diameter drills. A broken drill can result in significant downtime, so tool life should be approached conservatively. In this example, the drill will be changed after 17 parts. The drill life is then 68” (17 parts x 4” per part). The drill cost per part is $5.88 and can be calculated as follows:

cannulated formula 3

Comparing the drilling in the Swiss to using cannulated material, we find that using cannulated material does provide savings.

cannulated formula 4

Using the typical simple analysis, there is a savings of $1.49 per part using cannulated raw material. At 200 pieces per month, the annual savings would be $3,576. The savings are somewhat mediocre. If the part was already in production, the cost savings might justify changing to cannulated material.

But there is a far greater impact and benefit of using cannulated bar.

This driver, when made from solid bar, has 14.0 minutes in the main spindle and 3.0 minutes in the sub spindle. This would result in a production rate of 4.3 parts per hour as the main spindle operation is the pacing factor. The production rate in pieces per hour is calculated using the greater of the cycle time in the main spindle or sub spindle and the following equation:cannulated formula 5 updated

However, when using cannulated material, the time in main spindle is 8.0 minutes; cannulated drilling time of 6.0 minutes has been eliminated from the main spindle work. By using cannulated material, the production rate increases to 7.5 parts per hour. This would be an increase in efficiency of 74%. This increase in efficiency can be obtained without additional machine operators or equipment.

Let’s look at another example of a titanium implant.

Implant Example

cannulated screw

Exhibit 2: Cannulated Compression Screw, Ti 6Al 4V, 4 mm, 100mm length, 1.4 mm Cannulation, T15 Torx

Solid 0.250” titanium alloy for the screw in Exhibit 2 is $5.16 per foot while cannulated material is $44.49 per foot. Using the formula in Example 1, the raw material cost is $1.85 for the solid bar and $15.92 for the cannulated bar.

To determine the cost of drilling a shop rate of $100 per hour will be used along with a drilling feed rate of 0.8” per minute. Using these values and the formula above, the cost to drill the hole is $8.33.

Drills will again be changed after making 17 pieces, so the cost of drill bits will be $5.88 per piece; the same as in Example 1.

cannulated formula 6

In this example, the savings in using cannulated material versus solid bar is only $0.14. Even at high implant volumes and applying to a family of 4.0 mm diameter screws of various lengths, the material savings do not justify using cannulated raw material.

However, when one looks at the increase in production rate, it makes sense to use cannulated material. In this example, the main spindle time with solid bar was 12 minutes producing 5.0 parts per hour. With a feed rate of 0.8” per minute, the drill time of 5.0 minutes is eliminated from the work being done in the main spindle. Using cannulated raw material results in a production rate of 8.6 parts per hour, a 71% increase in productivity over 5.0 parts per hour using solid bar.

The increase in production rate is related by the ratio of drilling time to the total time in the main spindle. The greater this ratio, the greater the increase in production rates when using cannulated bar.

cannulated formula 7 updated

In the first example, the ratio was 6.0/14.0 = .42, which resulted in an increase from 4.3 parts per hour to 7.5 parts per hour, an improvement 74%. In the second example, the ratio was 5.0/12.0 = .41, which resulted in an increase of 71% going from 5.0 to 8.6 parts per hour. In these examples, the parts are somewhat long. If the implant in the second example was 45 mm in length, the ratio would be 2.8/9.8 = .29. The production rate would increase from 6.5 to 8.8 parts per hour. Even with a short part, using cannulated bar provides a production rate increase of 35%.

What’s the Impact on Product Launches?

How would increasing production affect a product launch? We can use the implant in the example above, a launch quantity of 24,000 screws and an average length of 65 mm. The production rate for a 65 mm screw is estimated at 5.5 parts per hour using solid bar and 8.7 parts per hour with cannulated bar. With three machines running 19 shifts per week (three shifts M-F, four weekend shifts) and 7.0 productive hours per shift, it would take 11 weeks using solid bar and seven weeks using cannulated bar. Using cannulated bar would shorten product production by four weeks.

For the contract manufacturer, using cannulated bar offers a significant benefit over a competitor using solid bar. Offering a shorter lead-time has potential opportunities for higher prices. Additionally, using fewer machines can save time and resources needed for capability runs and equipment qualification.

For the OEM, shortening production time can result in additional revenue by launching new products early. This not only increases sales, but can offer a competitive advantage.
The most significant impact for manufacturers that are currently gun drilling in their Swiss machines is the added capacity that can be achieved using cannulated material. Production rates can easily increase 50% to 70% when using cannulated bar. Conversion of current production to cannulated stock can add Swiss capacity without adding operators or machines. The added capacity can shorten backlogs and offers opportunity to add profitable shorter lead-time orders to fill the increased capacity.

For manufacturers, the gross profit resulting from one shift of parts running on a Swiss lathe can be $300 to $600. Machining capacity is usually the limiting factor as subsequent processes are typically batch processes such as vibratory finishing, cleaning, passivation, etc. Let’s assume one-third of the products being made on Swiss machines have gun drilled holes and can be converted to use cannulated material. If the manufacturer has 10 Swiss machines and is running 19 shifts per week, there are 9,500 shifts per year. Using a 50% increase in production rate using cannulated bar, there would become available an additional 1,567 shifts per year (9,500 shifts total x .33 converted to cannulated x .50 increase in production rate). The resulting profits from the added capacity made available by using cannulated bar would be $470,000 to $940,000.

Traditionally, the evaluation of using cannulated bar or solid bar only considered the difference in the cost of the raw material. As we have seen, there are other benefits. The increase in production rate when using cannulated rather than solid bar will shorten production time and can result in significant increases in manufacturing efficiency.



Ryan Thornburgh is the Business Development Manager of Precision Medical Technologies. He has over 10 years of experience with medical devices and a background in sales, management, operations, machining and quality. 

This email address is being protected from spambots. You need JavaScript enabled to view it. is the General Manager of Forécreu America, Inc. He has over 10 years of experience helping foreign-owned companies grow in the U.S. and a background in sales, marketing, finance and management.

This email address is being protected from spambots. You need JavaScript enabled to view it. is a consultant specializing in product development, operations, quality, supply chain, and M&A with expertise in low-cost sourcing, design transfer, design for manufacturability, special process validation, cleaning validation, additive manufacturing, failure analysis, and cost accounting.