Investment Casting through the ages

Investment casting, one of the oldest metallurgical arts, is the process of creating intricately detailed near-net-shape castings. Today, investment casting is used to produce precision components for spacecraft and jet engines using the latest advances in computer technology, robotics and countergravity casting techniques. Hitchiner Manufacturing has contributed to the art of investment casting with the development cutting-edge technology to produce the highest quality parts available today.

Replica of bronze sceptre from the Nahal Mishmar Hoard.

Early days of investment castings

The basic root of this technology dates back more than 4,000 years ago, to the land between the Tigrus and Euphrates Rivers known as Mesopotamia. Ancient artisans produced idols and ornaments using natural beeswax for patterns, clay for molds, and manually operated bellows for stoking furnaces. The artists and sculptors of ancient Egypt and Mesopotamia, the Han Dynasty in China, and the Benin civilization in Africa used the cire perdue or "lost wax" process of casting to produce their intricately detailed artwork of copper, bronze and gold. 

In Pre-Columbian Mexico, the Aztec goldsmiths used the lost wax process to create much of their elaborate jewelry. Unfortunately, few examples of this work survived; countless masterpieces were melted down into gold bars by the conquistadors to enrich the Spanish treasury. What we know of the Aztec's methods is found in the writings of Friar Bernardino de Sahagun, who spent 60 years intensively studying Aztec Mexico and learning their process. Of the few pieces that have survived, they demonstrate a great mastery of the process.

Late Cycladic (17th century BC) gold ibex sculpture about 10 cm long with lost-wax cast feet and head and repoussé body, from an excavation on Santorini

Brass smiths of Nigeria

In the city of Benin, Nigeria, where brass smiths make lost wax castings using a method passed down through generations, we can get a glimpse of the early history of the investment casting process.

The brass casters at Benin begin with a core of clay kneaded into a mass, shaped into the approximate size of the article to be made and allowed to dry thoroughly in the sun for several days. The brass smith then creates a pattern for the casting by covering a dried core with beeswax and carefully modeling it into the exact shape desired. Thus, each casting is a unique hand-formed work.

When the wax form is finished to the artist's satisfaction, it is covered in a coating of clay applied in layers. Before the pattern is fully sealed in this coating, a thin roll of wax is added to form a channel into which the molten metal will be poured. Layers of a thicker clay are then added, gradually investing, or covering, the form completely to create the mold. 

When a batch of molds has been created, dried and ready for casting. they are placed in a fire and heated so that the wax melts and can be poured off. The clay molds are further heated to a point where they are sufficiently fired to permit the pouring of the molten metal without causing the shell to burst. The molds are then taken from the fire and placed upright in spaded earth and the molten brass is poured into the open mold. Soon after casting, the molds are broken open, the shell knocked off and the final object is cleaned, filed and polished. Benin lost wax castings can be found in museums throughout the world.

Benin bronze

Perseus and the art of casting

Shortly after the dark ages in Europe, the industrious sculptor and goldsmith Benvenuto Cellini began to make use of the lost wax method of casting. He learned this process from the writings of the monk Theophilus Presbyter (circa 1100) whose Schedula Diversarum Artium is the earliest known foundry text. In Cellini's autobiography, considered to be one of the classics of literature, he describes in great detail the casting of his famous Perseus and the Head of Medusa. This three and a half ton statue was completed in 1554 and was unveiled at the Loggia dei Lanzi in Florence, Italy, where it stands to this day.

The investment casting process has been used in the arts by many civilizations for countless centuries, and was developed to a high degree of excellence, as is evident by many beautiful and finely detailed statues, jewelry and artifacts from antiquity that were created through this ancient process.

Perseus with the Head of Medusa by Benvenuto Cellini

Perseus with the Head of Medusa by Benvenuto Cellini

Investment casting in the modern era

Modern industry largely ignored investment casting until the early the twentieth century, when it was "rediscovered" by the dental profession for producing crowns and inlays. The first authenticated record of the use of investment castings in dentistry appears in a paper written by Dr. D. Philbrook of Council Bluffs, Iowa in 1897. However, the true significance of this process was not realized until the research of Dr. William H. Taggart of Chicago was published in 1907. Dr. Taggart not only developed and described a technique, he formulated a wax pattern compound of excellent properties, developed an investment material, and even invented an air pressure casting machine.

During World War II, with urgent military demands overtaxing the machine tool industry, investment casting provided a shortcut for producing precision parts and allowed for the use of specialized alloys which could not be readily shaped by alternative methods. During the post-war period, it expanded into many commercial and industrial uses where complex metal parts were needed. It was during this era that Hitchiner Manufacturing Company was founded at the Amoskeag Millyards of Manchester, NH.

Dr. William H. Taggart

Dr. William H. Taggart

Advances in investment casting at Hitchiner

Over the years, Hitchiner has developed a number of technological advances that helped to bring investment casting into the 21st Century, including the first of its exclusive countergravity casting processes, patented in the 1970s. The future of the investment casting process is very bright, in part due to the research and development commitment of Hitchiner Manufacturing Co., Inc. and Metal Casting Technology, Inc., a wholly owned R&D facility of Hitchiner Manufacturing Co., Inc.